Sec Form 3 Filing - Willett Peter Casimir @ Greenbrook TMS Inc. - 2024-01-01

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Willett Peter Casimir 2. Issuer Name and Ticker or Trading Symbol Greenbrook TMS Inc. [ GBNH] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Financial Officer (Last) (First) (Middle) C/O GREENBROOK TMS. 890 YONGE STREET, 7TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 01/01/2024 (Street) TORONTO, A6M4W3P4 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Options $ 5 ( 1 ) 03/31/2027 Common Shares 3,000 D Options $ 7.5 ( 2 ) 03/31/2028 Common Shares 2,000 D Options $ 10 ( 3 ) 10/03/2028 Common Shares 3,000 D Options $ 12.44 ( 5 ) ( 4 ) 03/27/2029 Common Shares 5,000 D Options $ 10.13 ( 7 ) ( 6 ) 02/03/2030 Common Shares 4,000 D Options $ 15.45 ( 9 ) ( 8 ) 02/17/2031 Common Shares 10,000 D Options $ 0.75 ( 10 ) 05/15/2033 Common Shares 75,000 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Willett Peter Casimir C/O GREENBROOK TMS. 890 YONGE STREET 7TH FLOOR TORONTO, A6M4W3P4 Chief Financial Officer Signatures /s/William Leonard, Attorney-in-Fact 01/02/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )These options were granted pursuant to the Company's Amended Employee Stock Option Plan (the "Stock Option Plan") as described in the Company's 2022 Meeting Information Circular, filed with the Securities and Exchange Commission on May 23, 2023. The options were granted on March 31, 2017 and vested over a three-year period, with one-third vesting on each of the 3 anniversaries of the date of the grant. As of the date hereof, all options are vested and exercisable. ( 2 )These options were granted pursuant to the Stock Option Plan on March 31, 2018 and vested over a three year period, with one-third vesting on each of the 3 anniversaries of the date of the grant. As of the date hereof, all options are vested and exercisable. ( 3 )These options were granted pursuant to the Stock Option Plan on October 3, 2018, with the first-third vesting on March 31, 2019 and the remaining two thirds vesting in equal parts on each of the 2 anniversaries of the initial vesting. As of the date hereof, all options are vested and exercisable. ( 4 )These options were granted pursuant to the Stock Option Plan on March 27, 2019 and vested over a three year period, with one-third vesting on each of the 3 anniversaries of the date of the grant. As of the date hereof, all options are vested and exercisable. ( 5 )Converted to USD based on the average daily exchange rate of the Bank of Canada reported on December 29, 2023. Each option may be exercised for a price of $16.45 Canadian dollars. ( 6 )These options were granted pursuant to the Stock Option Plan on February 3, 2020 and vested over a three year period, with one-third vesting on each of the 3 anniversaries of the date of the grant. As of the date hereof, all options are vested and exercisable. ( 7 )Converted to USD based on the average daily exchange rate of the Bank of Canada reported on December 29, 2023. Each option may be exercised for a price of $13.40 Canadian dollars. ( 8 )These options were granted pursuant to the Stock Option Plan on February 17, 2021 and will vest over a three year period, with one-third vesting on each of the 3 anniversaries of the date of the grant. As of the date hereof, 6,667 options are vested and exercisable. ( 9 )Converted to USD based on the average daily exchange rate of the Bank of Canada reported on December 29, 2023. Each option may be exercised for a price of $20.43 Canadian dollars. ( 10 )These options were granted pursuant to the Company's Omnibus Equity Incentive Plan as described in the Company's 2022 Meeting Information Circular, filed with the Securities and Exchange Commission on May 23, 2023, on May 15, 2023. Half of the options granted immediately vested while the remaining half vest over a two-year period, with one-quarter of the total amount vesting on each of the 2 anniversaries of the date of the grant. As of the date hereof, 37,500 options are vested and exercisable.

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