SECTION 16 POWER OF ATTORNEY

The undersigned hereby constitutes and appoints Bill Leonard, my true and
lawful attorneys-in-fact and agents, each acting alone, with full powers
of substitution, for me and in my name, place and stead, in any and all
capacities, to sign any and all Forms 3, 4 or 5 in connection with my
beneficial ownership of securities of Greenbrook TMS Inc. (the "Company")
that may be required of me pursuant to Section 16 of the Securities
Exchange Act of 1934 and the rules and regulations promulgated thereunder,
and to file the same and all other documents in connection therewith, with
the Securities and Exchange Commission, granting unto said attorneys-in-fact
and agents, each acting alone, full power and authority to do and perform
each and every act and thing requisite and necessary to be done in and
about the premises, as fully to all intents and purposes as I might or
could do in person, hereby ratifying and confirming all that said
attorneys-in-fact and agents, each acting alone, or his substitute,
may lawfully do or cause to be done by virtue hereof.

I declare that any act or thing lawfully done hereunder by my said
attorneys-in-fact and agents shall be binding on myself and my heirs,
legal and personal representatives, and assigns, whether the same shall
have been done before or after my death, or other revocation of this
instrument, unless and until reliable notice thereof shall have been
received by any party who, upon the faith of this instrument, accepts
my said attorneys-in-fact and agents as authorized to represent me.

This power of attorney and the authority of my attorneys-in-fact and
agents hereunder shall not terminate on my disability but shall remain
in full force and effect for so long as I am an officer or director of
the Company and for such time hereafter as may be necessary to file any
such reports.

IN WITNESS WHEREOF, I have hereunto set my hand and seal this 27th day
of January, 2024.

Name: /s/Juliana Elstad
         Juliana Elstad