RISK FACTORS

In addition to the other information contained in or incorporated by reference into this document, including the matters addressed under the caption “Cautionary Statement Regarding Forward-Looking Statements,” beginning on page [ — ] of this joint proxy statement/prospectus, Actavis shareholders should carefully consider the following risks in deciding whether to vote for the approval of the Actavis Share Issuance Proposal, and Forest stockholders should carefully consider the following risk factors in deciding whether to vote for the First Merger Proposal and the Merger-Related Named Executive Officer Compensation Proposal. You should also consider the other information in this document and the other documents incorporated by reference into this document. See “Where You Can Find More Information” beginning on page [ — ] of this joint proxy statement/prospectus.

Risks Related to the Transaction

Because the market price of Actavis ordinary shares will fluctuate, Forest stockholders cannot be sure of the market price of the Actavis ordinary shares they will receive.

As a result of the First Merger, each issued and outstanding share of Forest common stock, other than excluded shares and dissenting shares, will be converted into the right to receive the Standard Election Consideration. Alternatively, Forest stockholders will have the right to make either a cash election to receive the Cash Election Consideration, or a stock election to receive the Stock Election Consideration, for each of their Forest shares. Both the cash election and the stock election are subject to the proration and adjustment procedures, described under “ The Merger Agreement—Election and Proration Procedures; Procedures for Converting Shares of Forest Common Stock into Merger Consideration; Dissenter’s Rights ” beginning on page [ — ] of this joint proxy statement/prospectus, to cause the total amount of cash paid, and the total number of Actavis ordinary shares issued, in the First Merger to the holders of shares of Forest common stock (other than excluded shares), as a whole, to equal as nearly as practicable the total amount of cash and number of shares that would have been paid and issued if all of such shares of Forest common stock were converted into the Standard Election Consideration.

The market price of Actavis ordinary shares, which Forest stockholders may receive in the First Merger, will continue to fluctuate from the date of this joint proxy statement/prospectus through the date of the closing of the First Merger. Accordingly, at the time of the Forest special meeting, Forest stockholders will not know or be able to determine the market price of the Actavis ordinary shares they may receive upon completion of the First Merger. It is possible that, at the time of the closing of the First Merger, the shares of Forest common stock held by Forest stockholders may have a greater market value than the cash and the Actavis ordinary shares for which they are exchanged. The market price of Actavis ordinary shares on the date of the Forest special meeting may not be indicative of the market price of Actavis ordinary shares that Forest stockholders will receive upon completion of the First Merger. The market prices of Actavis ordinary shares and Forest common stock are subject to general price fluctuations in the market for publicly traded equity securities and have experienced volatility in the past. Stock price changes may result from a variety of factors, including general market and economic conditions and changes in the respective businesses, operations and prospects, and regulatory considerations of Actavis and Forest. Market assessments of the benefits of the Mergers and the likelihood that the Mergers will be completed, as well as general and industry specific market and economic conditions, may also impact market prices of Actavis ordinary shares and Forest common stock. Many of these factors are beyond Actavis’ and Forest’s control. You should obtain current market quotations for shares of Forest common stock and for Actavis ordinary shares.

Forest stockholders may receive a form of consideration different from what they elect.

Although each Forest stockholder may elect to receive all cash or all Actavis ordinary shares in the First Merger, the pool of cash and the Actavis ordinary shares available for all Forest stockholders will be a fixed

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percentage of the aggregate Merger Consideration at closing, and will not exceed the aggregate number of Actavis ordinary shares that would have been issued, and the aggregate amount of cash that would have been paid, to all of the holders of shares of Forest common stock had the election to receive 0.3306 of an Actavis ordinary share and $26.04 in cash been made with respect to each share of Forest common stock (other than excluded shares and dissenting shares). As a result, if the aggregate amount of shares with respect to which either cash elections or stock elections have been made would otherwise result in payments of cash or stock in excess of the maximum amount of cash or stock available, and a Forest stockholder has chosen the consideration election that exceeds the maximum available, such Forest stockholder will receive consideration in part in a form that such stockholder did not choose. This could result in, among other things, tax consequences that differ from those that would have resulted if such Forest stockholder had received the form of consideration that the stockholder elected (including the potential recognition of gain for federal income tax purposes if the stockholder receives cash). For illustrative examples of how the proration procedures would work in the event there is an oversubscription of the cash election or stock election in the First Merger, see “ The Merger Agreement—Election and Proration Procedures; Procedures for Converting Shares of Forest Common Stock into Merger Consideration; Dissenter’s Rights ” beginning on page [ — ] of this joint proxy statement/prospectus.

The market price for Actavis ordinary shares following the closing may be affected by factors different from those that historically have affected Forest common stock and Actavis ordinary shares.

Upon completion of the First Merger, holders of shares of Forest common stock (other than those who elect to receive all cash, and who do receive all cash, in the First Merger, and the holders of excluded shares and dissenting shares) will become holders of Actavis ordinary shares. Actavis’ businesses differ from those of Forest, and accordingly the results of operations of Actavis will be affected by some factors that are different from those currently affecting the results of operations of Forest. In addition, upon completion of the First Merger, holders of Actavis ordinary shares will become holders of shares in the combined company. The results of operation of the combined company may also be affected by factors different from those currently affecting Actavis. For a discussion of the businesses of Actavis and Forest and of some important factors to consider in connection with those businesses, see the documents incorporated by reference in this joint proxy statement/prospectus and referred to under “ Where You Can Find More Information ” beginning on page [ — ] of this joint proxy statement/prospectus.

Actavis and Forest must obtain required approvals and governmental and regulatory consents to consummate the Mergers, which if delayed, not granted or granted with unacceptable conditions, may delay or jeopardize the consummation of the Mergers, result in additional expenditures of money and resources and/or reduce the anticipated benefits of the Mergers.

The Mergers are subject to customary closing conditions. These closing conditions include, among others, the receipt of required approvals by the Forest stockholders and the Actavis shareholders, the clearances of the Mergers by certain governmental and regulatory authorities and the expiration or termination of applicable waiting periods under the HSR Act, and the antitrust and competition laws of certain foreign countries under which filings or approvals are or may be required. To the extent required, foreign investment filings will be made, though these are not closing conditions. The governmental agencies from which the parties will make these filings and seek certain of these approvals and consents have broad discretion in administering the governing regulations. Actavis and Forest can provide no assurance that all required approvals and consents will be obtained. Moreover, as a condition to their approval of the transaction, agencies may impose requirements, limitations or costs or require divestitures or place restrictions on the conduct of the business of the combined company after the closing. These requirements, limitations, costs, divestitures or restrictions could jeopardize or delay the effective time or reduce the anticipated benefits of the transaction. Further, no assurance can be given that the required shareholder and stockholder approvals will be obtained or that the required closing conditions will be satisfied, and, if all required consents and approvals are obtained and the closing conditions are satisfied, no assurance can be given as to the terms, conditions and timing of the approvals or clearances. If Actavis and Forest agree to any material requirements, limitations, costs, divestitures or restrictions in order to obtain any

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approvals or clearances required to consummate the transaction, these requirements, limitations, costs, divestitures or restrictions could adversely affect the combined company’s ability to integrate Actavis’ operations with Forest’s operations and/or reduce the anticipated benefits of the transaction. This could result in a failure to consummate the transactions or have a material adverse effect on the business and results of operations of the combined company. For additional information, see “ The Mergers—Regulatory Approvals Required for the Transaction ” beginning on page [ — ] of this joint proxy statement/prospectus.

The Merger Agreement may be terminated in accordance with its terms and the Mergers may not be completed.

The Merger Agreement contains a number of conditions that must be fulfilled to complete the Mergers. Those conditions include: the approval of the First Merger Proposal by Forest stockholders, approval of the Actavis Share Issuance Proposal by Actavis shareholders, receipt of requisite regulatory and antitrust approvals, absence of orders prohibiting completion of the Mergers, effectiveness of the registration statement of which this document is a part, approval of the Actavis ordinary shares to be issued to Forest stockholders for listing on the New York Stock Exchange, the continued accuracy of the representations and warranties of both parties subject to specified materiality standards, and the performance by both parties of their covenants and agreements. These conditions to the closing of the Mergers may not be fulfilled and, accordingly, the Mergers may not be completed. In addition, if the First Merger is not completed by August 17, 2014 (subject to extension to November 17, 2014, and subsequently to December 17, 2014, if the only conditions not satisfied or waived (other than those conditions that by their nature are to be satisfied at the Closing, which conditions shall be capable of being satisfied) are conditions relating to HSR clearance, other required filings and clearances under foreign antitrust laws, the absence of certain proceedings under antitrust laws and the absence of any orders or injunctions under antitrust laws), either Actavis or Forest may choose not to proceed with the Mergers. In addition, Actavis or Forest may elect to terminate the Merger Agreement in certain other circumstances, and the parties can mutually decide to terminate the Merger Agreement at any time prior to the consummation of the First Merger, before or after stockholder approval. See “ The Merger Agreement—Termination of the Merger Agreement; Termination Fees ” beginning on page [ — ] of this joint proxy statement/prospectus for a fuller description of these circumstances.

The Merger Agreement contains provisions that restrict Actavis’ ability to pursue alternatives to the Mergers and, in specified circumstances, could require Actavis to pay Forest a termination fee.

Under the Merger Agreement, Actavis is restricted, subject to certain exceptions, from soliciting, initiating, knowingly encouraging, discussing or negotiating, or furnishing information with regard to, any inquiry, proposal or offer for a competing acquisition proposal from any person or entity. Actavis may not terminate the Merger Agreement in order to enter into an agreement with respect to a superior proposal. If the Actavis board of directors (after consultation with Actavis’ financial advisors and legal counsel) determines that such proposal is more favorable to the Actavis shareholders than the Mergers and the Actavis board of directors recommends such proposal to the Actavis shareholders, Forest would be entitled to terminate the Merger Agreement. Under such circumstances, Actavis would be required to pay Forest a termination fee equal to $1.175 billion. These provisions could discourage a third party that may have an interest in acquiring all or a significant part of Actavis from considering or proposing that acquisition, even if such third party were prepared to pay consideration with a higher value than the value of the Merger Consideration. Additionally, in the event the Merger Agreement is terminated due to the failure of the Actavis shareholders to approve the Actavis Share Issuance Proposal at the Actavis EGM, Actavis would be required to pay Forest a fee of $335 million, increasing to $1.175 billion in certain circumstances. See “ The Merger Agreement—Termination of the Merger Agreement; Termination Fees ” beginning on page [ — ] of this joint proxy statement/prospectus.

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The Merger Agreement contains provisions that restrict Forest’s ability to pursue alternatives to the First Merger and, in specified circumstances, could require Forest to pay Actavis a termination fee.

Under the Merger Agreement, Forest is restricted, subject to certain exceptions, from soliciting, initiating, knowingly encouraging, discussing or negotiating, or furnishing information with regard to, any inquiry, proposal or offer for a competing acquisition proposal from any person or entity. Forest may not terminate the Merger Agreement in order to enter into an agreement with respect to a superior proposal. If the Forest board of directors (after consultation with Forest’s financial advisors and legal counsel) determines that such proposal is more favorable to the Forest stockholders than the Mergers and the Forest board of directors recommends such proposal to the Forest stockholders, Actavis would be entitled to terminate the Merger Agreement. Under such circumstances, Forest would be required to pay Actavis a termination fee equal to $875 million. These provisions could discourage a third party that may have an interest in acquiring all or a significant part of Forest from considering or proposing that acquisition, even if such third party were prepared to pay consideration with a higher value than the value of the Merger Consideration. Additionally, in the event the Merger Agreement is terminated due to the failure of the Forest stockholders to approve the First Merger Proposal at the Forest special meeting, Forest would be required to pay Actavis a fee of $250 million, increasing to $875 million in certain circumstances. See “ The Merger Agreement—Termination of the Merger Agreement; Termination Fees ” beginning on page [ — ] of this joint proxy statement/prospectus.

While the First Merger is pending, Actavis and Forest will be subject to business uncertainties that could adversely affect their business.

Uncertainty about the effect of the First Merger on employees, customers and suppliers may have an adverse effect on Forest and Actavis. These uncertainties may impair Actavis’ and Forest’s ability to attract, retain and motivate key personnel until the First Merger is consummated and for a period of time thereafter, and could cause customers, suppliers and others who deal with Actavis and Forest to seek to change existing business relationships with Actavis and Forest. Employee retention may be challenging during the pendency of the Mergers, as certain employees may experience uncertainty about their future roles. If key employees depart because of issues related to the uncertainty and difficulty of integration or a desire not to remain with the businesses, the business of the combined company following the Mergers could be seriously harmed. In addition, the Merger Agreement restricts Forest and, to a lesser extent, Actavis, from taking specified actions until the First Merger occurs without the consent of the other party. These restrictions may prevent Actavis or Forest from pursuing attractive business opportunities that may arise prior to the completion of the First Merger. See “ The Merger Agreement—Covenants and Agreements ” beginning on page [ — ] of this joint proxy statement/prospectus for a description of the restrictive covenants applicable to Actavis and Forest.

Forest directors and officers may have interests in the First Merger different from the interests of Forest stockholders and Actavis shareholders.

Certain of the directors and executive officers of Forest negotiated the terms of the Merger Agreement, and the Forest board of directors recommended that the stockholders of Forest vote in favor of the merger-related proposals. These directors and executive officers may have interests in the First Merger that are different from, or in addition to, those of Forest stockholders and Actavis shareholders. These interests include, but are not limited to, the continued employment of certain executive officers of Forest by Actavis, the continued service of certain directors of Forest as directors of Actavis, the treatment in the First Merger of stock options, restricted stock, restricted stock units, bonus awards, change of control employment agreements and other rights held by Forest directors and executive officers, and the indemnification of former Forest directors and officers by Actavis. Forest stockholders and Actavis shareholders should be aware of these interests when they consider their respective board of directors’ recommendation that they vote in favor of the merger-related proposals.

The Forest board of directors was aware of these interests when it declared the advisability of the Merger Agreement, determined that it was fair to the Forest stockholders and recommended that the Forest stockholders

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adopt the Merger Agreement. The interests of Forest directors and executive officers are described in more detail in the section of this document entitled “ The Mergers—Interests of Forest’s Directors and Executive Officers in the Transaction ” beginning on page [ — ] of this joint proxy statement/prospectus.

Forest stockholders will have a reduced ownership and voting interest after the First Merger and will exercise less influence over management.

Forest stockholders currently have the right to vote in the election of the board of directors of Forest and on other matters affecting Forest. Upon the completion of the First Merger, each Forest stockholder who receives Actavis ordinary shares will become a shareholder of Actavis with a percentage ownership of Actavis that is smaller than the stockholder’s percentage ownership of Forest. It is currently expected that the former stockholders of Forest as a group will receive shares in the First Merger constituting approximately 35% of the outstanding Actavis ordinary shares immediately after the First Merger. Because of this, Forest stockholders will have less influence on the management and policies of Actavis than they now have on the management and policies of Forest.

Actavis ordinary shares to be received by Forest stockholders as a result of the First Merger will have rights different from the shares of Forest common stock.

Upon completion of the First Merger, the rights of former Forest stockholders who become Actavis shareholders will be governed by the memorandum of association and articles of association of Actavis and by Irish law. The rights associated with shares of Forest common stock are different from the rights associated with Actavis ordinary shares. Material differences between the rights of stockholders of Forest and the rights of shareholders of Actavis include differences with respect to, among other things, distributions, dividends, repurchases and redemptions, dividends in shares / bonus issues, the election of directors, the removal of directors, the fiduciary and statutory duties of directors, conflicts of interests of directors, the indemnification of directors and officers, limitations on director liability, the convening of annual meetings of shareholders and special shareholder meetings, notice provisions for meetings, the quorum for shareholder meetings, the adjournment of shareholder meetings, the exercise of voting rights, shareholder action by written consent, shareholder suits, shareholder approval of certain transactions, rights of dissenting shareholders, anti-takeover measures and provisions relating to the ability to amend the articles of association. See “ Comparison of the Rights of Holders of Actavis Ordinary Shares and Forest Common Stock ” beginning on page [ — ] of this joint proxy statement/prospectus for a discussion of the different rights associated with Actavis ordinary shares and Forest common stock.

The opinions of Actavis’ and Forest’s financial advisors will not reflect changes in circumstances between the original signing of the Merger Agreement and the completion of the First Merger.

Actavis and Forest have not obtained updated opinions from their respective financial advisors as of the date of this document and do not expect to receive updated opinions prior to the completion of the First Merger. Changes in the operations and prospects of Actavis or Forest, general market and economic conditions and other factors that may be beyond the control of Actavis or Forest, and on which Actavis’ and Forest’s financial advisors’ opinions were based, may significantly alter the value of Forest or the prices of Actavis ordinary shares or Forest common stock by the time the First Merger is completed. The opinions do not speak as of the time the First Merger will be completed or as of any date other than the date of such opinions. Because Actavis’ and Forest’s financial advisors will not be updating their opinions, the opinions will not address the fairness of the Merger Consideration from a financial point of view at the time the First Merger is completed. Actavis’ board of directors’ recommendation that Actavis shareholders vote “FOR” the Actavis Share Issuance Proposal and Forest’s board of directors’ recommendation that Forest stockholders vote “FOR” the First Merger Proposal, however, are made as of the date of this document. For a description of the opinions that Actavis and Forest received from their respective financial advisors, please refer to “ The Mergers—Opinion of Actavis’ Financial Advisor ” and “ The Mergers—Opinion of Forest’s Financial Advisor ” beginning on pages [ — ] and [ — ], respectively, of this joint proxy statement/prospectus.

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Irish resident or ordinarily resident holders of Forest common stock may be subject to Irish tax on chargeable gains on the cancellation of their shares of Forest common stock.

Forest stockholders that are resident or ordinarily resident in Ireland for Irish tax purposes, or Forest stockholders that hold their shares of Forest common stock in connection with a trade carried on by such persons through an Irish branch or agency, will, subject to the availability of any exemptions and reliefs, generally be subject to Irish tax on chargeable gains arising on the cancellation of their shares of Forest common stock pursuant to the First Merger. The receipt by such a Forest stockholder of cash only pursuant to a cash election will be treated as a disposal of his or her shares of Forest common stock for the purposes of Irish capital gains tax or corporation tax on chargeable gains (as applicable) (“Irish CGT”) and such holder may, subject to the availability of any exemptions and reliefs, realize a chargeable gain (or allowable loss). On the basis that the First Merger is treated as a ‘scheme of reconstruction or amalgamation’ for Irish CGT purposes and subject to certain conditions the following treatment should apply: the receipt by such a Forest stockholder of Actavis ordinary shares and cash (including any cash received in lieu of a fractional Actavis ordinary share) will be treated as a part disposal of his or her shares of Forest common stock for Irish CGT purposes in respect of the cash consideration received. This may, subject to the availability of any exemptions and reliefs, give rise to a chargeable gain (or allowable loss) for the purposes of Irish CGT in respect of the cash received. The Actavis ordinary shares received should be treated as the same asset as the cancelled shares of Forest common stock and as acquired at the same time and for the same consideration as those cancelled shares of Forest common stock as adjusted for the part of the consideration attributable to the part disposal in respect of the receipt of cash. If such a Forest stockholder makes a stock election and receives only Actavis ordinary shares on the cancellation of his or her shares of Forest common stock, the cancellation and receipt should not be treated as a disposal of shares of Forest common stock for Irish CGT purposes but instead the Actavis ordinary shares received should be treated as the same asset as those cancelled shares of Forest common stock and as acquired at the same time and for the same consideration as those cancelled shares of Forest common stock.

See “ Certain Tax Consequences of the Mergers—Irish Tax Considerations—Irish Tax on Chargeable Gains ” beginning on page [ — ] of this joint proxy statement/prospectus for more information.

Legal proceedings in connection with the Mergers, the outcomes of which are uncertain, could delay or prevent the completion of the Mergers.

Since the announcement of the Merger Agreement on February 18, 2014, a number of putative stockholder class action complaints have been filed in New York and Delaware courts against Forest, the members of its board of directors, Actavis, US Holdings, Merger Sub 1 and Merger Sub 2 challenging the proposed Mergers. The actions allege that members of the Forest board of directors breached their fiduciary duties by agreeing to sell Forest for inadequate consideration and pursuant to an inadequate process, and that Actavis, US Holdings, Merger Sub 1 and Merger Sub 2 aided and abetted these alleged breaches. Among other remedies, the plaintiffs seek to enjoin the Mergers. Such legal proceedings could delay or prevent the Mergers from becoming effective within the agreed upon timeframe. See “ Litigation Relating to the Mergers ” beginning on page [ — ] of this joint proxy statement/ prospectus.

Actavis ordinary shares received by means of a gift or inheritance could be subject to Irish capital acquisitions tax.

Irish capital acquisitions tax (“CAT”) (currently levied at a rate of 33% above certain tax-free thresholds) could apply to a gift or inheritance of Actavis ordinary shares irrespective of the place of residence, ordinary residence, or domicile of the parties. This is because Actavis ordinary shares will be regarded as property situated in Ireland for Irish CAT purposes. The person who receives the gift or inheritance has primary liability for CAT. See “ Certain Tax Consequences of the Mergers—Irish Tax Considerations—Capital Acquisitions Tax (CAT) ” beginning on page [ — ] of this joint proxy statement/ prospectus.

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Risks Related to the Business of the Combined Company

Actavis and Forest may fail to realize all of the anticipated benefits of the Mergers or those benefits may take longer to realize than expected. The combined company may also encounter significant difficulties in integrating the two businesses. The Mergers may result in adverse tax consequences to Actavis.

The ability of Actavis and Forest to realize the anticipated benefits of the transaction will depend, to a large extent, on the combined company’s ability to integrate the two businesses. The combination of two independent businesses is a complex, costly and time-consuming process. As a result, Actavis and Forest will be required to devote significant management attention and resources to integrating their business practices and operations. The integration process may disrupt the businesses and, if implemented ineffectively, would restrict the realization of the full expected benefits. The failure to meet the challenges involved in integrating the two businesses and to realize the anticipated benefits of the transaction could cause an interruption of, or a loss of momentum in, the activities of the combined company and could adversely affect the results of operations of the combined company.

In addition, the overall integration of the businesses may result in material unanticipated problems, expenses, liabilities, competitive responses, loss of customer relationships, and diversion of management’s attention. The difficulties of combining the operations of the companies include, among others:

Many of these factors will be outside of the control of Actavis or Forest and any one of them could result in increased costs, decreases in the amount of expected revenues and diversion of management’s time and energy, which could materially impact the business, financial condition and results of operations of the combined company. In addition, even if the operations of the businesses of Actavis and Forest are integrated successfully, the full benefits of the transaction may not be realized, including the synergies, cost savings or sales or growth opportunities that are expected. These benefits may not be achieved within the anticipated time frame, or at all. Or, additional unanticipated costs may be incurred in the integration of the businesses of Actavis and Forest. All of these factors could cause dilution to the earnings per share of Actavis, decrease or delay the expected accretive effect of the transaction, and negatively impact the price of Actavis ordinary shares. As a result, we cannot assure you that the combination of Actavis and Forest will result in the realization of the full benefits anticipated from the transaction.

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Combining the businesses of Actavis and Forest may be more difficult, costly or time-consuming than expected, which may adversely affect Actavis’ results and negatively affect the value of Actavis’ ordinary shares following the First Merger.

Actavis and Forest have entered into the Merger Agreement because each believes that the Mergers will be beneficial to it and its respective shareholders and stockholders and that combining the businesses of Actavis and Forest will produce benefits and cost savings. If Actavis is not able to successfully combine the businesses of Actavis and Forest in an efficient and effective manner, the anticipated benefits and cost savings of the Mergers may not be realized fully, or at all, or may take longer to realize than expected, and the value of Actavis ordinary shares may be affected adversely.

In addition, the actual integration may result in additional and unforeseen expenses, and the anticipated benefits of the integration plan may not be realized. Actual synergies, if achieved, may be lower than and may take longer to achieve than anticipated. If Actavis is not able to adequately address integration challenges, Actavis may be unable to successfully integrate Actavis’ and Forest’s operations or to realize the anticipated benefits of the integration of the two companies.

Actavis and Forest will incur direct and indirect costs as a result of the Mergers.

Actavis and Forest will incur substantial expenses in connection with completing the Mergers, and over a period of time following the completion of the Mergers, Actavis further expects to incur substantial expenses in connection with coordinating the businesses, operations, policies and procedures of Actavis and Forest. While Actavis has assumed that a certain level of transaction and coordination expenses will be incurred, there are a number of factors beyond Actavis’ control that could affect the total amount or the timing of these transaction and coordination expenses. Many of the expenses that will be incurred, by their nature, are difficult to estimate accurately. These expenses may exceed the costs historically borne by Actavis and Forest.

Actavis expects that, following the Mergers, Actavis will have significantly less cash on hand than the sum of cash on hand of Actavis and Forest prior to the Mergers. This reduced amount of cash could adversely affect Actavis’ ability to grow.

Actavis is expected to have significantly less cash and cash equivalents on hand than the approximately $1,362.1 million of combined cash and cash equivalents of the two companies, after giving effect to the Aptalis Acquisition (as defined in “ Unaudited Pro Forma Combined Financial Information ” beginning on page [ — ] of this joint proxy statement/prospectus), as of December 31, 2013, and would have on a pro forma basis, giving effect to the Mergers as if they had been consummated on December 31, 2013, no cash and cash equivalents. See “ Unaudited Pro Forma Combined Financial Information ” beginning on page [ — ] of this joint proxy statement/prospectus. Although the management of Actavis believes that it will have access to cash sufficient to meet Actavis’ business objectives and capital needs, the lessened availability of cash and cash equivalents following the consummation of the Mergers could constrain Actavis’ ability to grow its business. Actavis’ financial position following the Mergers could also make it vulnerable to general economic downturns and industry conditions, and place it at a competitive disadvantage relative to its competitors that have more cash at their disposal. In the event that Actavis does not have adequate capital to maintain or develop its business, additional capital may not be available to Actavis on a timely basis, on favorable terms, or at all.

If the First Merger is consummated, Actavis will incur a substantial amount of debt to finance the cash portion of the Merger Consideration, which could restrict its ability to engage in additional transactions or incur additional indebtedness.

In connection with the First Merger, Actavis expects to (i) borrow up to $2.0 billion under the senior credit facilities, (ii) issue and sell up to $2.0 billion in aggregate principal amount of senior unsecured notes and (iii) under certain circumstances, borrow up to $4.0 billion in loans under the bridge facility. Following the

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completion of the First Merger, the combined company will have a significant amount of indebtedness outstanding. On a pro forma basis, giving effect to the incurrence of indebtedness as described in “ The Merger Agreement—Financing Relating to the Transaction ” beginning on page [ — ] of this joint proxy statement/prospectus, the consolidated indebtedness of Actavis would be approximately $17,877.6 million as of December 31, 2013. See “ Unaudited Pro Forma Combined Financial Information ” beginning on page [ — ] of this joint proxy statement/prospectus. This substantial level of indebtedness could have important consequences to Actavis’ business, including making it more difficult to satisfy its obligations, increasing its vulnerability to general adverse economic and industry conditions, limiting its flexibility in planning for, or reacting to, changes in its business and the industry in which it operates and restricting Actavis from pursuing certain business opportunities. These limitations could reduce the benefits Actavis expects to achieve from the First Merger or impede its ability to engage in future business opportunities or strategic acquisitions.

In addition, under certain circumstances, Actavis could be required to make an offer to repurchase Forest’s senior notes shortly after the completion of the First Merger at a price equal to 101% of the aggregate principal amount of the notes, plus accrued and unpaid interest thereon to the date of repurchase. If any such offer is accepted, Actavis intends to fund the required repurchase from a combination of available cash on hand of Actavis and additional financing. Actavis cannot assure you that any such financing will be available in an amount sufficient to fund prepayment of Forest’s senior notes or at all or that the terms of any such financing will be favorable. In addition, any such financing may include restrictive covenants that, among other things, limit Actavis’ ability to engage in certain business transactions or incur additional indebtedness.

Actavis’ and Forest’s actual financial positions and results of operations may differ materially from the unaudited pro forma financial data included in this joint proxy statement/prospectus.

The pro forma financial information contained in this joint proxy statement/prospectus is presented for illustrative purposes only and may not be an indication of what Actavis’ financial position or results of operations would have been had the transaction been completed on the dates indicated. The pro forma financial information has been derived from the audited and unaudited historical financial statements of Actavis and Forest and certain adjustments and assumptions have been made regarding the combined company after giving effect to the transaction. The assets and liabilities of Forest have been measured at fair value based on various preliminary estimates using assumptions that Actavis management believes are reasonable utilizing information currently available. The process for estimating the fair value of acquired assets and assumed liabilities requires the use of judgment in determining the appropriate assumptions and estimates. These estimates may be revised as additional information becomes available and as additional analyses are performed. Differences between preliminary estimates in the pro forma financial information and the final acquisition accounting will occur and could have a material impact on the pro forma financial information and the combined company’s financial position and future results of operations.

In addition, the assumptions used in preparing the pro forma financial information may not prove to be accurate, and other factors may affect Actavis’ financial condition or results of operations following the closing. Any potential decline in Actavis’ financial condition or results of operations may cause significant variations in the share price of Actavis. See “ Unaudited Pro Forma Combined Financial Information ” beginning on page [ — ] of this joint proxy statement/prospectus.

The Mergers may not be accretive and may cause dilution to Actavis’ earnings per share, which may negatively affect the market price of Actavis ordinary shares.

Although Actavis currently anticipates that the Mergers will be accretive to earnings per share (on an adjusted earnings basis) from and after the Mergers, this expectation is based on preliminary estimates, which may change materially.

As described and based on the assumptions in the section of this joint proxy statement/prospectus entitled “ The Mergers—Consideration to Forest Stockholders ” beginning on page [ — ], Actavis expects to issue or reserve

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for issuance approximately 99 million Actavis ordinary shares in connection with completion of the First Merger. The issuance of these new Actavis ordinary shares could have the effect of depressing the market price of Actavis ordinary shares.

In addition, Actavis could also encounter additional transaction-related costs or other factors such as the failure to realize all of the benefits anticipated in the Mergers. All of these factors could cause dilution to Actavis’ earnings per share or decrease or delay the expected accretive effect of the Mergers and cause a decrease in the market price of Actavis ordinary shares.

The Internal Revenue Service (the “IRS”) may not agree that Actavis is a foreign corporation for U.S. federal tax purposes.

Although Actavis is incorporated in Ireland, the IRS may assert that Actavis should be treated as a U.S. corporation for U.S. federal tax purposes pursuant to Section 7874. For U.S. federal tax purposes, a corporation generally is classified as either a U.S. corporation or a foreign corporation by reference to the jurisdiction of its organization or incorporation. Because Actavis is an Irish incorporated entity, it would generally be classified as a foreign corporation under these rules. Section 7874 provides an exception to this general rule under which a foreign incorporated entity may, in certain circumstances, be treated as a U.S. corporation for U.S. federal tax purposes.

Under Section 7874, a corporation created or organized outside the United States (i.e., a foreign corporation) will nevertheless be treated as a U.S. corporation for U.S. federal tax purposes when (i) the foreign corporation directly or indirectly acquires substantially all of the assets held directly or indirectly by a U.S. corporation (including the indirect acquisition of assets of the U.S. corporation by acquiring all the outstanding shares of the U.S. corporation), (ii) the shareholders of the acquired U.S. corporation hold at least 80% (by either vote or value) of the shares of the foreign acquiring corporation after the acquisition by reason of holding shares in the U.S. acquired corporation (including the receipt of the foreign corporation’s shares in exchange for the U.S. corporation’s shares), and (iii) the foreign corporation’s “expanded affiliated group” does not have substantial business activities in the foreign corporation’s country of organization or incorporation relative to such expanded affiliated group’s worldwide activities. For purposes of Section 7874, multiple acquisitions of U.S. corporations by a foreign corporation, if treated as part of a plan or series of related transactions, may be treated as a single acquisition. If multiple acquisitions of U.S. corporations are treated as a single acquisition, all shareholders of the acquired U.S. corporations would be aggregated for purposes of the test set forth above concerning such shareholders holding at least 80% (by either vote or value) of the shares of the foreign acquiring corporation after the acquisitions by reason of holding shares in the acquired U.S. corporations.

On October 1, 2013, Actavis acquired all of the capital stock of Actavis, Inc., a Nevada corporation, and Warner Chilcott plc, a company incorporated under the laws of Ireland (the “Warner Chilcott Transaction”). Actavis believes that, in the Warner Chilcott Transaction, the Actavis, Inc. shareholders received less than 80% (by both vote and value) of the Actavis shares and consequently that the test set forth above to treat Actavis as a foreign corporation was satisfied. However, the law and Treasury regulations promulgated under Section 7874 are relatively new and somewhat unclear, and thus we cannot assure you that the IRS will agree that the ownership requirements to treat Actavis as a foreign corporation were met in the Warner Chilcott Transaction. Moreover, even if such ownership requirements were met in the Warner Chilcott Transaction, the IRS may assert that, even though the Mergers are separate transactions from the Warner Chilcott Transaction, the Mergers may be integrated with the Warner Chilcott Transaction. In the event the IRS were to prevail with such assertion, Actavis would be treated as a U.S. corporation for U.S. federal tax purposes. Actavis has received opinions from Latham & Watkins and PwC to the effect that Actavis should not be treated as a domestic corporation for U.S. federal income tax purposes as a result of the Mergers, but we cannot assure you that the IRS will agree with this position and/or would not successfully challenge Actavis’ status as a foreign corporation. If such a challenge by the IRS were successful, significant adverse tax consequences would result for Actavis.

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See “ Certain Tax Consequences of the Mergers—U.S. Federal Income Tax Considerations—U.S. Federal Income Tax Consequences of the Mergers—Tax Consequences to Actavis ” beginning on page [ — ] of this joint proxy statement/prospectus for a full discussion of the application of Section 7874 to the transaction.

Section 7874 likely will limit Actavis’ and its U.S. affiliates’ ability to utilize certain U.S. tax attributes of Forest and its U.S. affiliates to offset certain U.S. taxable income, if any, generated by the Mergers or certain specified transactions for a period of time following the Mergers.

Following the acquisition of a U.S. corporation by a foreign corporation, Section 7874 can limit the ability of the acquired U.S. corporation and its U.S. affiliates to utilize certain U.S. tax attributes such as net operating losses to offset U.S. taxable income resulting from certain transactions. Based on the limited guidance available, Actavis believes that this limitation applies to Actavis and its U.S. affiliates following the Warner Chilcott Transaction and as a result, Actavis currently does not expect that it or its U.S. affiliates (including Forest and its U.S. affiliates after the Mergers) will be able to utilize certain U.S. tax attributes of Forest and its U.S. affiliates to offset their U.S. taxable income, if any, resulting from certain specified taxable transactions. See “ Certain Tax Consequences of the Mergers—U.S. Federal Income Tax Considerations—U.S. Federal Income Tax Consequences of the Mergers—Tax Consequences to Actavis ” beginning on page [ — ] of this joint proxy statement/prospectus.

Actavis’ status as a foreign corporation for U.S. federal tax purposes could be affected by a change in law.

Actavis believes that, under current law, it is treated as a foreign corporation for U.S. federal tax purposes. However, changes to the inversion rules in Section 7874 or the U.S. Treasury Regulations promulgated thereunder or other IRS guidance could adversely affect Actavis’ status as a foreign corporation for U.S. federal tax purposes, and any such changes could have prospective or retroactive application to Actavis, Forest, their respective stockholders, shareholders and affiliates, and/or the Mergers. In addition, recent legislative proposals have aimed to expand the scope of U.S. corporate tax residence, and such legislation, if passed, could have an adverse effect on Actavis. For example, in March 2014, the President of the United States proposed legislation which would amend the anti-inversion rules. Although its application is limited to transactions closing after 2014, no assurance can be given that proposal will not be changed in the legislative process and be enacted to apply to prior transactions.

Future changes to U.S. and foreign tax laws could adversely affect Actavis.

The U.S. Congress, the Organisation for Economic Co-operation and Development and other Government agencies in jurisdictions where Actavis and its affiliates do business have had an extended focus on issues related to the taxation of multinational corporations. One example is in the area of “base erosion and profit shifting,” where payments are made between affiliates from a jurisdiction with high tax rates to a jurisdiction with lower tax rates. As a result, the tax laws in the United States and other countries in which Actavis and its affiliates do business could change on a prospective or retroactive basis, and any such changes could adversely affect Actavis and its affiliates (including Forest and its affiliates after the Mergers).

If the Mergers do not qualify as a reorganization under Section 368(a) of the Code or are otherwise taxable to U.S. holders of Forest common stock, then such holders may be required to pay substantial U.S. federal income taxes.

It is intended that, for U.S. federal income tax purposes, the Mergers, taken together, shall (1) qualify as a reorganization within the meaning of Section 368(a) of the Code and (2) not result in gain being recognized by U.S. holders of Forest common stock immediately prior to the effective time of the First Merger under Section 367(a) of the Code (other than any such shareholder that would be a “five-percent transferee shareholder” (within the meaning of Treasury Regulations Section 1.367(a)-3(c)(5)(ii)) of Actavis following the Mergers that does not enter into a five-year gain recognition agreement in the form provided in Treasury

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Regulations Section 1.367(a)-8), and the parties intend to report the Mergers in a manner consistent with the Intended Tax Treatment. However, there are significant factual and legal uncertainties concerning whether the Mergers will qualify for the Intended Tax Treatment. For example, Section 367(a) of the Code and the applicable Treasury regulations promulgated thereunder provide that where a U.S. shareholder exchanges stock in a U.S. corporation for stock in a non-U.S. corporation in a transaction that would otherwise qualify as a reorganization within the meaning of Section 368(a) of the Code, the U.S. shareholder is required to recognize gain, but not loss, realized on such exchange unless certain requirements are met. There are significant factual and legal uncertainties concerning the determination of certain of these requirements. In addition, the closing of the Mergers is not conditioned upon the receipt of an opinion of counsel that the Mergers will qualify for the Intended Tax Treatment, and no assurance can be given that the IRS will not challenge the Intended Tax Treatment or that a court would not sustain a challenge by the IRS. Moreover, none of Actavis, US Holdings, Forest or either of the Merger Subs intends to request a ruling from the IRS regarding the U.S. federal income tax consequences of the Mergers. If at the effective time of the Mergers the fair market value of Forest were found to exceed that of Actavis, or other requirements for the non-recognition of gain under Section 367(a) of the Code are not met or any requirement of Section 368 is not satisfied, a U.S. holder of Forest common stock would recognize gain (but may not be able to recognize loss) based on the amount such U.S. holder realizes in the Mergers.

For a further discussion, see “ Certain Tax Consequences of the Mergers—U.S. Federal Income Tax Considerations—U.S. Federal Income Tax Consequences of the Mergers—Tax Consequences to U.S. Holders ” beginning on page [ — ] of this joint proxy statement/prospectus.

Transfers of Actavis ordinary shares, other than by means of the transfer of book-entry interests in the Depository Trust Company (“DTC”), may be subject to Irish stamp duty.

For the majority of transfers of Actavis ordinary shares, there will not be any Irish stamp duty. Transfers of Actavis ordinary shares effected by means of the transfer of book-entry interests in DTC are not subject to Irish stamp duty. However, if you hold your Actavis ordinary shares directly rather than beneficially through DTC, any transfer of your Actavis ordinary shares could be subject to Irish stamp duty (currently at the rate of 1% of the higher of the price paid or the market value of the shares acquired). A shareholder who directly holds shares may transfer those shares into his or her own broker account to be held through DTC (or vice versa) without giving rise to Irish stamp duty provided that there is no change in the ultimate beneficial ownership of the shares as a result of the transfer and the transfer is not in contemplation of a sale of the shares by a beneficial owner to a third party.

Payment of Irish stamp duty is generally a legal obligation of the transferee. The potential for stamp duty could adversely affect the price of your shares. See “ Certain Tax Consequences of the Mergers—Irish Tax Considerations—Stamp Duty ” beginning on page [ — ] of this joint proxy statement/prospectus.

In certain limited circumstances, dividends paid by Actavis may be subject to Irish dividend withholding tax.

In certain limited circumstances, Irish dividend withholding tax (“DWT”) (currently at a rate of 20%) may arise in respect of dividends, if any, paid on Actavis ordinary shares. A number of exemptions from DWT exist pursuant to which shareholders resident in the U.S. and shareholders resident in the countries listed in Annex E attached to this joint proxy statement/prospectus (the “Relevant Territories”) may be entitled to exemptions from DWT.

See “ Certain Tax Consequences of the Mergers—Irish Tax Considerations—Withholding Tax on Dividends (DWT) ” beginning on page [ — ] of this joint proxy statement/prospectus and, in particular, please note the requirement to complete certain relevant Irish Revenue Commissioners DWT forms (“DWT Forms”) in order to qualify for many of the exemptions.

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Dividends paid in respect of Actavis ordinary shares that are owned by a U.S. resident and held through DTC will not be subject to DWT provided the address of the beneficial owner of such shares in the records of the broker holding such shares is recorded as being in the U.S. (and such broker has further transmitted the relevant information to a qualifying intermediary appointed by Actavis). Similarly, dividends paid in respect of Actavis ordinary shares that are held outside of DTC and are owned by a former Forest stockholder who is a resident of the U.S. will not be subject to DWT if such shareholder has provided a completed IRS Form 6166 or a valid DWT Form to Actavis’ transfer agent to confirm its U.S. residence and claim an exemption. Shareholders resident in other Relevant Territories may also be eligible for exemption from DWT on dividends paid in respect of their shares provided they have furnished valid DWT Forms to their brokers (in respect of shares held through DTC) (and such broker has further transmitted the relevant information to a qualifying intermediary appointed by Actavis) or to Actavis’ transfer agent (in respect of shares held outside of DTC). However, other shareholders may be subject to DWT, which if you are such a shareholder could adversely affect the price of your shares. See “ Certain Tax Consequences of the Mergers—Irish Tax Considerations—Withholding Tax on Dividends (DWT) ” beginning on page [ — ] of this joint proxy statement/prospectus for more information on DWT.

Risks Related to Actavis’ Business

You should read and consider risk factors specific to Actavis’ businesses that will also affect the combined company after the Mergers. These risks are described in Part I, Item 1A of Actavis’ Annual Report on Form 10-K for the fiscal year ended December 31, 2013, and in other documents that are incorporated by reference into this document. See “ Where You Can Find More Information ” beginning on page [ — ] of this joint proxy statement/prospectus for the location of information incorporated by reference in this joint proxy statement/prospectus.

Risks Related to Forest’s Business

You should read and consider risk factors specific to Forest’s business that will also affect the combined company after the Mergers. These risks are described in Part I, Item 1A of Forest’s Annual Report on Form 10-K for the fiscal year ended March 31, 2013, and in other documents that are incorporated by reference into this document. See “ Where You Can Find More Information ” beginning on page [ — ] of this joint proxy statement/prospectus for the location of information incorporated by reference in this joint proxy statement/prospectus.

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