Doctors at a child gender clinic raised concerns about the use of puberty blockers 15 years ago – an issue that was also discussed by staff last year.
An internal review conducted in 2005, obtained by BBC Newsnight, says some clinicians felt pressured to refer patients for the treatment too quickly.
Staff at the Gender Identity Development Service (GIDS) raised serious safeguarding issues last year.
The Trust which runs the clinic said the report was "no longer relevant".
GIDS, which is run by the Tavistock and Portman NHS Foundation Trust, is a specialised unit for young people who have difficulties with their gender identity.
In 2005, the Trust's then medical director, adult psychiatrist Dr David Taylor, conducted a review into the service – then called the Gender Identity Development Unit.
He reported that colleagues at the Trust were working hard to provide good care for patients, but highlighted concerns about some aspects of their treatment.
The document details concerns raised by some clinicians at that time about alleged pressure on staff to refer patients for treatment with puberty blockers, a lack of a robust evidence base underpinning this treatment, and the apparently troubled backgrounds of some young people referred. These included past sexual abuse and trauma.
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Newsnight obtained the 2005 review via the Freedom of Information Act, a move which the Tavistock and Portman NHS Foundation Trust resisted. It argued disclosure of the document would "adversely impact on the Trust's ability to provide effective and safe services to its patients".
But the Information Commissioner's Office ruled that the document's publication was in the public interest.
In his 2005 report Dr Taylor, who left in 2011 after 30 years, made a series of recommendations for improvements to the service – which in 2005 was much smaller, receiving tens of referrals per year rather than thousands.
Dr Taylor called for the service to monitor patients after leaving, for more research into this area of healthcare, and for staff to be supported if faced with pressure to refer for treatments when they thought it was inappropriate.
In his report, which was published in 2006, he said puberty blockers might be the best course of action for some, but added that in his view young people needed a period of explorative therapy first.
The document also detailed concerns from some staff about the speed at which some young people were being referred for treatment with puberty blockers.
These drugs stop a young person's body developing, with the aim of helping to relieve gender dysphoria – distress caused when a person's gender identity does not match their biological sex. The NHS now recognises that little is known about their long term side effects.
Concerns about the use of puberty blockers were subsequently raised by other staff in the internal 2019 review of the service.
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