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): February 9, 2018

Alder BioPharmaceuticals, Inc.

(Exact name of registrant as specified in its charter)

(425) 205-2900

Registrant’s telephone number, including area code:

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:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company  ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

Item 8.01 Other Events.

Alder BioPharmaceuticals, Inc. (“Alder”) is filing this Current Report on Form 8-K to provide a copy of the legal opinion of Cooley LLP relating to the legality of Alder’s common stock, par value $0.0001 per share, to be offered and sold pursuant to Alder’s Registration Statement on Form S-3 (File No. 333-216199) and the related prospectus supplement, dated February 9, 2018, and filed with the U.S. Securities and Exchange Commission pursuant to Rule 424 under the Securities Act.

In addition, Alder has updated certain risk factors it previously disclosed in its current and periodic reports as filed with the Securities and Exchange Commission from time to time. A copy of the updated risk factors is attached to this Current Report on Form 8-K as Exhibit 99.1 and incorporated by reference herein.

Forward Looking Statements

This Current Report on Form 8-K contains forward-looking statements, including, without limitation, statements relating to: the continued development and clinical, therapeutic and commercial potential of eptinezumab; the availability of clinical trial data; and future regulatory submissions. Words such as “may,” “will,” “should,” “could,” “would,” “expects,” “plans,” “anticipates,” “believes,” “estimates,” “projects,” “predicts,” “potential” and similar expressions identify forward-looking statements, but the absence of these words or expressions does not necessarily mean that a statement is not forward-looking. In addition, any statements that refer to expectations, projections or other characterizations of future events or circumstances are forward-looking statements. The forward-looking statements in this Current Report on Form 8-K are based upon our current plans, assumptions, beliefs, expectations, estimates and projections, and involve substantial risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in the forward-looking statements due to these risks and uncertainties as well as other factors, which include, without limitation: risks related to the potential failure of eptinezumab to demonstrate safety and efficacy in clinical testing; the availability of data at the expected times; the clinical, therapeutic and commercial value of eptinezumab; risks and uncertainties related to regulatory review and approval processes and our compliance with applicable legal and regulatory requirements; the uncertain timing and level of expenses associated with the development of eptinezumab; the sufficiency of our capital and other resources; market competition; changes in economic and business conditions; and other factors discussed in the revised risk factors is attached to this Current Report on Form 8-K, and our other filings with the Securities and Exchange Commission. The forward-looking statements made in this Current Report on Form 8-K speak only as of the date of this Current Report on Form 8-K. We expressly disclaims any duty, obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in the our expectations with regard thereto or any change in events, conditions or circumstances on which any such statements are based.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

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.