UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of Earliest Event Reported): July 26, 2015

ALLERGAN PLC

(Exact name of registrant as specified in its charter)

(862) 261-7000

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On July 26, 2015, Allergan plc and Naurex Inc. issued a joint press release announcing entry into of an Agreement and Plan of Merger pursuant to which Allergan plc has agreed to acquire Naurex Inc. A copy of the joint press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

(d) Exhibits

Allergan Cautionary Statement Regarding Forward-Looking Statements

Statements contained in this communication that refer to Allergan’s estimated or anticipated future results or other non-historical facts are “forward-looking statements” that reflect Allergan’s current perspective of existing trends and information as of the date of this communication. Forward looking statements generally will be accompanied by words such as “anticipate,” “believe,” “plan,” “could,” “should,” “estimate,” “expect,” “forecast,” “outlook,” “guidance,” “intend,” “may,” “might,” “will,” “possible,” “potential,” “predict,” “project,” or other similar words, phrases or expressions. Such forward-looking statements include, but are not limited to, statements about the benefits of the Naurex acquisition, including future financial and operating results, Allergan’s or Naurex’s plans, objectives, expectations and intentions and the expected timing of completion of the transaction. It is important to note that Allergan’s goals and expectations are not predictions of actual performance. Actual results may differ materially from Allergan’s current expectations depending upon a number of factors affecting Allergan’s business, Naurex’s business and risks associated with acquisition transactions. These factors include, among others, the inherent uncertainty associated with financial projections; successful closing of the Naurex acquisition; subsequent integration of the Naurex acquisition; the ability to obtain required regulatory approvals for the transaction (including the approval of antitrust authorities necessary to complete the acquisition), the timing of obtaining such approvals and the risk that such approvals may result in the imposition of conditions that could adversely affect the combined company or the expected benefits of the transaction; the risk that a condition to closing of the Naurex acquisition may not be satisfied on a timely basis or at all; the failure of the proposed transaction to close for any other reason; the impact of competitive products and pricing; the risks of fluctuations in foreign currency exchange rates; the risks and uncertainties normally incident to the pharmaceutical industry, including product liability claims and the availability of product liability insurance on reasonable terms; periodic dependence on a small number of products for a material source of net revenue or income; variability of trade buying patterns; the timing and success of product launches; the difficulty of predicting the timing or outcome of product development efforts and regulatory agency approvals or actions, if any; market acceptance of and continued demand for Allergan’s products; costs and efforts to defend or enforce intellectual property rights; difficulties or delays in manufacturing; the availability and pricing of third party sourced products and materials; successful compliance with governmental regulations applicable to Allergan’s and Naurex’s facilities, products and/or businesses; changes in the laws and regulations affecting, among other things, pricing and reimbursement of pharmaceutical products; the loss of key senior management or scientific staff; and such other risks and uncertainties detailed in Allergan’s periodic public filings with the SEC, including but not limited to Allergan’s Annual Report on Form 10-K for the year ended December 31, 2014, Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2015 (such periodic public filings having been filed under the “Actavis plc” name), and from time to time in Allergan’s other investor communications. Except as expressly required by law, Allergan disclaims any intent or obligation to update or revise these forward-looking statements.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EXHIBIT INDEX