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Aileen O’Brien vs. transgender people

Aileen O’Brien is a British psychiatrist and anti-transgender activist. O’Brien is affiliated with anti-trans hate group Society for Evidence-Based Gender Medicine (SEGM) and Clinical Advisory Network on Sex and Gender (CAN-SG).

Background

Aileen Ann O’Brien was born in January 1970. According to a submitted biography by O’Brien:

  • A George’s graduate myself, I did an intercalated BSc in sociology and philosophy. I have combined clinical and academic work since training as a clinical lecturer at St George’s.
  • I am now a Reader in Psychiatry and Education. I am joint Consultant for the Psychiatric Intensive Care Unit and section 136 suite at South West London and St. George’s Mental Health NHS Trust.
  • My academic commitments include being the psychiatry undergraduate teaching lead at St George’s, one of the personal tutor leads and the Athena Swan Lead.
  • I am also the education and training lead for the National Association of Psychiatric Intensive Care Units (NAPICU) and I am one of the debate and analysis editors of the British Journal of Psychiatry.

O’Brien has served as education lead for the National Association of Psychiatric Intensive Care Units (NAPICU) and is an honorary Consultant Psychiatrist for Burntwood Villas, at South West London and St George’s Mental Health NHS Trust.

Anti-transgender activism

O’Brien has served as membership secretary for Clinical Advisory Network on Sex and Gender (CAN-SG) and has appeared in a number of their videos. O’Brien has also signed a number of open letters and letters to the editor, noting an affiliation with CAN-SG.

O’Brien was announced as a speaker at Rethinking Youth Gender Medicine, a 2026 conference held by hate group SEGM and CAN-SG.

Anti-trans coverage

Staff report (October 20, 2023). Webinar #CANSGDoNoHarm. Clinical Advisory Network on Sex and Gender https://can-sg.org/2023/10/20/webinar-cansgdonoharm/

Staff report (October 4, 2023). Introducing the Clinical Advisory Network on Sex and Gender. Clinical Advisory Network on Sex and Gender https://can-sg.org/introducing-the-clinical-advisory-network-on-sex-and-gender/

Selected writing by O’Brien

Cohen, Deborah (December 18, 2025). “This is why the trial is necessary”: experts behind the puberty blockers study respond to mounting opposition. BMJ, 391, r2660. https://doi.org/10.1136/bmj.r2660

Aileen O’Brien and signatories (December 18, 2025). Open Letter from clinicians to Wes Streeting on the PATHWAYS Puberty Blocker Trial. Clinical Advisory Network on Sex and Gender https://can-sg.org/2025/12/18/open-letter-to-wes-streeting-on-the-pathways-puberty-blockers-trial/

Aileen O’Brien and signatories (December 2, 2025). Letter to PATHWAYS trial regulators December 2025. Clinical Advisory Network on Sex and Gender https://can-sg.org/letter-to-pathways-trial-regulators-december-2025/

Aileen O’Brien and signatories (March 2025). Risks of Puberty Blockers in Children: A Call for Ethical Review. Clinical Advisory Network on Sex and Gender https://can-sg.org/can-sg-letter-to-puberty-blocker-trial-researchers-sponsors-and-regulators-about-ethical-concerns/

Aileen O’Brien and signatories (April 15, 2024). Label Use of Puberty Blockers in Children. https://downloads.regulations.gov/FDA-2023-P-3767-0654/attachment_1.pdf

Feinmann, Jane (2024). Transgender care: doctors are advised to return to “ordinary best practice.” BMJ, q742. https://doi.org/10.1136/bmj.q742

Aileen O’Brien and signatories (December 31, 2023). Parents must hold schools to account on gender. The Guardian https://www.theguardian.com/theobserver/commentisfree/2023/dec/31/parents-must-hold-schools-to-account-on-gender-observer-letters

Block, Jennifer (February 23, 2023). Gender dysphoria in young people is rising—and so is professional disagreement. BMJ, p382. https://doi.org/10.1136/bmj.p382

Aileen O’Brien and signatories (February 23, 2023). Open Letter to NHS chiefs: The importance of the word “woman” in communication about women’s health. Clinical Advisory Network on Sex and Gender https://can-sg.org/2023/02/23/open-letter-to-nhs-chiefs-the-importance-of-the-word-woman/

Dyer, Clare (2022). Tavistock to face possible clinical negligence claims over gender identity service. BMJ, o2016. https://doi.org/10.1136/bmj.o2016

Media

Clinical Advisory Network on Sex and Gender with Aileen O’Brien, Alice Sullivan, David Pilgrim, Lisa Littman, and Daniel Kodsi (October 28, 2025). Are Academics Allowed To Talk About Sex? https://vimeo.com/1132094539

Clinical Advisory Network on Sex and Gender with Aileen O’Brien, Louise Irvine, Stella O’Malley, and Bob Withers (October 4, 2023, uploaded 2025). Introducing the Clinical Advisory Network on Sex & Gender. https://vimeo.com/985797407 also on YouTube https://www.youtube.com/watch?v=3S-s1GWCxNE

Resources

YouTube (youtube.com)

X/Twitter (x.com)

Facebook (facebook.com)

ResearchGate (researchgate.net)

City St George’s University of London (sgul.ac.uk)

National Association of Psychiatric Intensive Care Units (napicu.org.uk)

Muck Rack (muckrack.com)