Exhibit 99.1

Dear Recipient,

We are just finishing up in Vancouver and are writing to share some of the positive news and feedback from the 18th Congress of the International Headache Society (“IHC”). As you may know, IHC is an international organization that brings together colleagues, industry partners and international scientists and clinicians to showcase advancements in headache science, education and management.

We had a number of encouraging individual meetings at IHC with migraine thought leaders to solicit expert understanding and feedback on attributes that positively differentiate eptinezumab for migraine prevention. We are pleased that they share our enthusiasm about the benefits of eptinezumab and its potential to change the current migraine treatment paradigm. Many expressed significant support for the infusion mode of administration, particularly the inherent advantages associated with the procedure. This included migraine specialists who are “interventionalists” that are familiar with infusion administration and prefer procedures that promote patient adherence and maximize product control and consistency of delivery. All of this reinforced eptinezumab’s highly competitive and differentiated profile.

Here are some examples of what we are hearing from the physician experts:

At IHC, Alder BioPharmaceuticals^® made seven presentations that highlighted key clinical data and analyses for eptinezumab, our monoclonal antibody and investigational product candidate for migraine prevention. Eptinezumab is the only monoclonal antibody administered by quarterly infusion in development that allows for 100% of the dose available to selectively and potently inhibit CGRP.ⁱ Eptinezumab is currently in Phase 3 clinical trials, including PROMISE 1 and PROMISE 2, to assess its efficacy and safety in migraine prevention. To date, more than 1,600 people have been treated with eptinezumab in clinical trials.

Alder also sponsored a satellite symposium, “Expert Perspectives: Migraine Prevention for Highly Impacted Patients”, led by luminaries in migraine including Drs. Richard Lipton, Merle Diamond and Stewart Tepper and chaired by our own Dr. Roger Cady. Key highlights from the symposium, which was extremely well-attended, included:

The presentation materials for the symposium are available on the Investors section of Alder’s website at this link.

As the only anti-CGRP administered by quarterly infusion in development, eptinezumab has the opportunity to address this significant unmet need for highly impacted migraine patients. The data presented from both Alder’s Phase 3 PROMISE 1 study and its Phase 2b study support eptinezumab’s clinical profile as a potential first-of-its-kind, highly differentiated infusion therapy to prevent migraine, including:

With the close of another successful IHC, we are more excited than ever and reiterate our commitment to transforming the treatment of migraine. Importantly, we remain on track to complete our BLA submission in the second half of 2018 and look forward to providing additional updates as we continue to make progress in anticipation of a commercial launch of eptinezumab.

As always, please feel free to reach out if you have any questions or would like to discuss any of the above in greater detail.

Thank you for your continued support.

Best,

Forward Looking Statements: This communication contains forward-looking statements, including, without limitation, statements relating to: the continued development and clinical, therapeutic and commercial potential of eptinezumab; the limitations of existing preventive migraine treatment options and the need for new effective preventive migraine treatment options; the impact of the data and results presented at IHC, including the potential benefits of eptinezumab and belief that the referenced results may represent a new standard for migraine prevention; the advantages of eptinezumab’s infusion mode of administration; Alder’s commitment to transforming the treatment of migraine; the planned regulatory submission for eptinezumab and the timing thereof; future updates; and the anticipated commercialization of eptinezumab. Words such as “will,” “would,” “encouraging,” “anticipation,” “potential,” “change,” “opportunity,” “support,” “need,” “improvement,” “address,” “change,” “towards,” “continue,” “benefits,” “advantages,” “on track,” “look forward,” or other similar expressions, identify forward-looking statements, but the absence of these words 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 communication are based upon Alder’s 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; Alder’s ability to conduct clinical trials and studies of eptinezumab sufficient to achieve a positive completion; the availability of data at the expected times; the clinical, therapeutic and commercial value of eptinezumab; risks and uncertainties related to regulatory application, review and approval processes and Alder’s compliance with applicable legal and regulatory requirements; risks and uncertainties relating to the manufacture of eptinezumab; Alder’s ability to obtain and protect intellectual property rights, and operate without infringing on the intellectual property rights of others; the uncertain timing and level of expenses associated with Alder’s development and commercialization activities; the sufficiency of Alder’s capital and other resources; market competition; changes in economic and business conditions; and other factors discussed under the caption “Risk Factors” in Alder’s Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2017, which was filed with the Securities and Exchange Commission (SEC) on August 8, 2017, and is available on the SEC’s website at www.sec.gov. Additional information will also be set forth in Alder’s other reports and filings it will make with the SEC from time to time. The forward-looking statements made in this communication speak only as of the date of this communication. Alder 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 Alder’s expectations with regard thereto or any change in events, conditions or circumstances on which any such statements are based.