SEC Form DEFA14A filed by Collegium Pharmaceutical Inc.

Step 1: Go to www.envisionreports.com/COLL. Step 2: Click on Cast Your Vote or Request Materials. Step 3: Follow the instructions on the screen to log in. www.envisionreports.com/COLL Online Go to www.envisionreports.com/COLL or scan the QR code — login details are located in the shaded bar below. Shareholder Meeting Notice 044C3B Important Notice Regarding the Availability of Proxy Materials for the Collegium Pharmaceutical, Inc. Meeting to be Held on May 15, 2025 Under Securities and Exchange Commission rules, you are receiving this notice that the proxy materials for the annual shareholders’ meeting are available on the Internet. Follow the instructions below to view the materials and vote online or request a copy. The items to be voted on and location of the annual meeting are on the reverse side. Your vote is important! This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. The 2025 proxy statement and 2024 annual report to shareholders is available at: Obtaining a Copy of the Proxy Materials – If you want to receive a copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. Please make your request as instructed on the reverse side on or before May 2, 2025 to facilitate timely delivery. 2NOT Easy Online Access — View your proxy materials and vote. When you go online, you can also help the environment by consenting to receive electronic delivery of future materials. The Sample Company Step 4: Make your selections as instructed on each screen for your delivery preferences. Step 5: Vote your shares.

Here’s how to order a copy of the proxy materials and select delivery preferences: Current and future delivery requests can be submitted using the options below. If you request an email copy, you will receive an email with a link to the current meeting materials. PLEASE NOTE: You must use the number in the shaded bar on the reverse side when requesting a copy of the proxy materials. — Internet – Go to www.envisionreports.com/COLL. Click Cast Your Vote or Request Materials. — Phone – Call us free of charge at 1-866-641-4276. — Email – Send an email to [email protected] with “Proxy Materials Collegium Pharmaceutical, Inc.” in the subject line. Include your full name and address, plus the number located in the shaded bar on the reverse side, and state that you want a paper copy of the meeting materials. To facilitate timely delivery, all requests for a paper copy of proxy materials must be received by May 2, 2025. Collegium Pharmaceutical, Inc.’s Annual Meeting of Shareholders will be held on May 15, 2025 virtually via live webcast meetnow.global/MZQSZJF at 8:30 a.m. Eastern Time. Proposals to be voted on at the meeting are listed below along with the Board of Directors’ recommendations. The Board of Directors recommends a vote FOR all the nominees listed and FOR Proposal 2, ONE YEAR for Proposal 3 and FOR Proposals 4 and 5: 1. Election of Rita Balice-Gordon, Ph.D., Garen Bohlin, John Fallon M.D., John Freund, M.D., Vikram Karnani, Nancy Lurker, Carlos Paya and Gino Santini as directors to hold office until the 2026 Annual Meeting. 2. Approval of, on an advisory basis, the compensation of the Company’s named executive officers 3. To indicate, on an advisory basis, the preferred frequency of shareholder advisory votes on the compensation of the Company’s named executive officers 4. Ratification of the appointment of Deloitte & Touche LLP as the company’s independent registered public accounting firm for the fiscal year ending December 31, 2025 5. To approve the Collegium Pharmaceutical, Inc. 2025 Equity Incentive Plan PLEASE NOTE – YOU CANNOT VOTE BY RETURNING THIS NOTICE. To vote your shares you must vote online or request a paper copy of the proxy materials to receive a proxy card. Shareholder Meeting Notice