COLLEGIUM PHARMACEUTICAL, INC

Securities Authorized for Issuance Under Equity Compensation Plans

The following table contains information about our equity compensation plans as of December 31, 2023.

The number of shares reserved for issuance under the 2014 Stock Incentive Plan automatically increases on January 1st each year, starting on January 1, 2016 and continuing through January 1, 2025, by an amount equal to four percent (4%) of the total number of shares of our capital stock outstanding on December 31st of the immediately preceding calendar year. Notwithstanding the foregoing, our Board may act prior to January 1st of a given year to provide that there will be no January 1st increase in the maximum number of shares that may be issued in respect of awards under the 2014 Stock Incentive Plan or that the increase in the maximum number of shares that may be issued in respect of awards for such year will be a lesser number of shares of common stock than would otherwise occur pursuant to the preceding sentence.

The number of shares reserved for issuance under the 2015 Employee Stock Purchase Plan automatically increases on January 1st each year, starting on January 1, 2016 and ending on December 31, 2025, by an amount equal to the least of: (a) 400,000 shares; (b) one percent (1%) of the total number of shares of our common stock outstanding on January 1st of each year; and (c) a number determined by our Board.

Shareholder Proposals and Director Nominations for 2025 Annual** Meeting of Shareholders**

Proposals of shareholders intended to be presented at our 2025 Annual Meeting of Shareholders must be submitted in accordance with the procedures outlined in Rule 14a-8 of the Exchange Act so that any such proposals are received by us no later than December 13, 2024, which is 120 calendar days prior to the first anniversary of the date on which our proxy statement was released to shareholders in connection with the annual meeting, in order to be included in our proxy statement and form of proxy relating to the 2025 Annual Meeting of Shareholders, unless the date of the 2025 Annual Meeting of Shareholders is changed by more than 30 days from the anniversary of the annual meeting, in which case the deadline for such proposals will be a reasonable time before we begin to print and send our proxy materials. These proposals must comply with the requirements as to form and substance established by the SEC for such proposals in order to be included in the proxy statement.

In addition, our bylaws establish an advance notice procedure for nominations for election to our Board and other matters that shareholders wish to present for action at an annual meeting other than those to be included in our proxy statement. In general, notice must be received at our principal executive offices not less than 90 calendar days before nor more than 120 calendar days before the one-year anniversary of the previous year’s annual meeting of shareholders. Therefore, to be presented at our 2025 Annual Meeting of Shareholders, such a proposal must be received by us no earlier than January 16, 2025 and no later than February 15, 2025. However, if the date of the annual meeting is more than 30 days earlier or more than 60 days later than such anniversary date, notice must be received no earlier than the close of business 120 calendar days prior to such annual meeting and no later than the close of business on the later of 90 days prior to such annual meeting or, if the first public announcement of the date of such annual meeting is less than 100 days prior to the date of such annual meeting, then such notice must be received by the tenth day following the day on which public announcement of the date of such meeting was first made by us. In addition, to comply with the universal proxy rules, shareholders who intend to solicit proxies in support of director nominees other than the Company’s nominees must provide notice by the same deadline noted herein to submit a notice of nomination for consideration at the 2025 Annual Meeting. Such notice must comply with the additional requirements of Rule 14a-19(b).

Any proposals we do not receive in accordance with the above standards will not be voted on at the 2025 Annual Meeting of Shareholders. Shareholders are advised to review our bylaws which also specify requirements as to the form and content of a shareholder’s notice.

Any proposals, notices or information about proposed director candidates should be sent to:

Collegium Pharmaceutical, Inc.

100 Technology Center Drive, Suite 300

Stoughton, MA 02072

Attention: Corporate Secretary

Email: skuhlmann@collegiumpharma.com

Delivery of Documents to Shareholders Sharing an Address

The SEC has adopted rules known as “householding” that permit companies and intermediaries (such as brokers) to deliver one set of proxy materials to multiple shareholders residing at the same address. This process enables us to reduce our printing and distribution costs and reduce our environmental impact. Householding is available to both registered shareholders and beneficial owners of shares held in street name.

Registered Shareholders

If you are a registered shareholder and have consented to householding, then we will deliver or mail one Notice or set of our proxy materials, as applicable, for all registered shareholders residing at the same address. Your consent will continue unless you revoke it, which you may do at any time by providing notice to our Corporate Secretary by telephone at (781) 713-3699 or by mail at 100 Technology Center Drive, Suite 300, Stoughton, MA 02072. In addition, the Company will promptly deliver, upon written or oral request to the address or telephone number above, a separate copy of the annual report, proxy statement, or Notice to a shareholder at a shared address to which a single copy of the documents was delivered.

If you are a registered shareholder who has not consented to householding, then we will continue to deliver or mail Notices or copies of our proxy materials, as applicable, to each registered shareholder residing at the same address. You may elect to participate in householding and receive only one Notice or set of proxy materials, as applicable, for all registered shareholders residing at the same address by providing notice to the Company as described above.

Street Name Holders

Shareholders who hold their shares through a brokerage may elect to participate in householding, or revoke their consent to participate in householding, by contacting their respective brokers.

Annual Report

This proxy statement is accompanied by our 2023 Annual Report to Shareholders, which includes our Annual Report on Form 10-K for the fiscal year ended December 31, 2023. The 2023 Form 10-K includes our audited financial statements. We have filed the 2023 Form 10-K with the SEC, and it is available free of charge at the SEC’s website at www.sec.gov and on our website at ir.collegiumpharma.com/sec-filings. In addition, upon written request to our Corporate Secretary at 100 Technology Center Drive, Suite 300, Stoughton, MA 02072, we will mail a paper copy of our 2023 Form 10-K, including the financial statements and the financial statement schedules, to you free of charge.

Other Matters

We do not know of any business that will be presented for consideration or action by the shareholders at the Annual Meeting other than that described in this proxy statement. If, however, any other business is properly brought before the meeting, shares represented by proxies will be voted in accordance with the best

judgment of the persons named in the proxies or their substitutes. All shareholders are urged to complete, sign and return the proxy card.

01 - Rita Balice-Gordon, Ph.D. 02 - Garen Bohlin 03 - Gwen Melincoff For Against Abstain For Against Abstain For Against Abstain 1UPX 04 - John Fallon M.D. 05 - John Freund, M.D. 06 - Neil F. Mcfarlane 07 - Joseph Ciaffoni 08 - Michael Heffernan, R.Ph. 09 - Gino Santini The Sample Company Using a black ink pen, mark your votes with an X as shown in this example. Please do not write outside the designated areas. 03YSMC + + A Proposals – The Board of Directors recommends a vote FOR all the nominees listed and FOR Proposals 2 and 3. 1. Election of Rita Balice-Gordon, Ph.D., Garen Bohlin, Gwen Melincoff, John Fallon M.D., John Freund, M.D., Neil F. Mcfarlane, Joseph Ciaffoni, Michael Heffernan, R.Ph. and Gino Santini as directors to hold office until the 2025 Annual Meeting: For Against Abstain Please sign exactly as name(s) appears hereon. Joint owners should each sign. When signing as attorney, executor, administrator, corporate officer, trustee, guardian, or custodian, please give full title. Date (mm/dd/yyyy) — Please print date below. Signature 1 — Please keep signature within the box. Signature 2 — Please keep signature within the box. B Authorized Signatures — This section must be completed for your vote to be counted. — Date and Sign Below q IF VOTING BY MAIL, SIGN, DETACH AND RETURN THE BOTTOM PORTION IN THE ENCLOSED ENVELOPE. q Annual Meeting Proxy Card For Against Abstain 2. Approval of, on an advisory basis, the compensation of the Company’s named executive officers. 3. Ratification of the appointment of Deloitte & Touche LLP as the company’s independent registered public accounting firm for the fiscal year ending December 31, 2024. MR A SAMPLE DESIGNATION (IF ANY) ADD 1 ADD 2 ADD 3 ADD 4 ADD 5 ADD 6 ENDORSEMENT_LINE______________ SACKPACK_____________ 1234 5678 9012 345 MMMMMMMMM MMMMMMMMMMMMMMM 611696 MR A SAMPLE (THIS AREA IS SET UP TO ACCOMMODATE 140 CHARACTERS) MR A SAMPLE AND MR A SAMPLE AND MR A SAMPLE AND MR A SAMPLE AND MR A SAMPLE AND MR A SAMPLE AND MR A SAMPLE AND MR A SAMPLE AND C 1234567890 J N T C123456789 MMMMMMMMMMMM MMMMMMM 000000000.000000 ext 000000000.000000 ext 000000000.000000 ext 000000000.000000 ext 000000000.000000 ext 000000000.000000 ext If no electronic voting, delete QR code and control # Δ ≈ 000001 Online Go to www.envisionreports.com/COPI or scan the QR code — login details are located in the shaded bar below. Save paper, time and money! Sign up for electronic delivery at www.envisionreports.com/COPI Phone Call toll free 1-800-652-VOTE (8683) within the USA, US territories and Canada You may vote online or by phone instead of mailing this card. Your vote matters – here’s how to vote!

Small steps make an impact. Help the environment by consenting to receive electronic delivery, sign up at www.envisionreports.com/COPI Notice of 2024 Annual Meeting of Shareholders Virtually via live webcast meetnow.global/MWVTLQP Proxy Solicited by Board of Directors for Annual Meeting — May 16, 2024 Joseph Ciaffoni and Shirley Kuhlmann, or any of them, each with the power of substitution, are hereby authorized to represent and vote the shares of the undersigned, with all the powers which the undersigned would possess if personally present, at the Annual Meeting of Shareholders of Collegium Pharmaceutical, Inc. to be held on May 16, 2024 or at any postponement or adjournment thereof. Shares represented by this proxy will be voted by the shareholder. If no such directions are indicated, the Proxies will have authority to vote FOR all director nominees and FOR Proposals 2 and 3. In their discretion, the Proxies are authorized to vote upon such other business as may properly come before the meeting. (Items to be voted appear on reverse side) Proxy — Collegium Pharmaceutical, Inc. q IF VOTING BY MAIL, SIGN, DETACH AND RETURN THE BOTTOM PORTION IN THE ENCLOSED ENVELOPE. q C Non-Voting Items + + Change of Address — Please print new address below. Comments — Please print your comments below. The 2024 Annual Meeting of Shareholders of Collegium Pharmaceutical, Inc. will be held on Thursday, May 16, 2024, at 8:30 a.m. (Eastern Time), virtually via live webcast at meetnow.global/MWVTLQP. To access the virtual meeting, you must have the information that is printed in the shaded bar located on the reverse side of this form. 2024 Annual Meeting Admission Ticket 2024 Annual Meeting of Collegium Pharmaceutical, Inc. Shareholders Thursday, May 16, 2024, 8:30 a.m. Eastern Time Virtually via live webcast meetnow.global/MWVTLQP