The High Court had previously said children under 16 with gender dysphoria can only consent to the use of hormone-blocking treatments if they understand the “immediate and longterm consequences”.
The judges said it was “highly unlikely” that a child aged 13 or under would be able to consent to the treatment, and that it was “doubtful” a child of 14 or 15 would understand the consequences.
But the Tavistock and Portman NHS Foundation Trust, which runs the UK’s only gender identity development service for children, brought an appeal against the ruling in June.
And in yesterday’s judgment, the Court OFAPPEAL said it was inappropriate for the High Court to give the guidance, finding it is for doctors to exercise their judgment about whether their patients can properly consent.
Keira Bell, 24, was given the hormone treatment at 16 when she thought she may want to become a boy, and has since struggled with her health as she “de-transitioned” back into a woman.
She said: “I am obviously disappointed with the ruling of the court and especially that it did not grapple with the significant risk of harm that children are exposed to by being given powerful experimental drugs.
“I am surprised and disappointed that the court was not concerned that children as young as 10 have been put on a pathway to sterilisation.
It has shone a light into the dark corners of a medical scandal that is harming children and harmed me.
“It’s a fantasy and deeply concerning that any doctor could believe a 10-year-old could consent to the loss of their fertility.”
Hormone blockers pause the physical changes of puberty, such as breast development or facial hair. It is not known whether the blockers affect the development of the teenage brain or children’s bones.
Side effects may also include hot flushes, fatigue and mood alterations.
Ms Bell said she believed the medical service had become “politicised” and would be seeking permission to appeal to the Supreme Court.
In their ruling, the Lord Chief Justice Lord Burnett, with Sir Geoffrey Vos and Lady Justice King, said: “The court was not in a position to generalise about the capability of persons of different ages to understand what is necessary for them to be competent to consent to the administration of puberty blockers.
“It placed patients, parents and clinicians in a very difficult position.”
A Tavistock and Portman spokesman said: “We welcome the Court of Appeal’s judgment on behalf of the young people who require the Gender Identity Development Service and our dedicated staff.
“The judgment upholds established legal principles which respect the ability of our clinicians to engage actively and thoughtfully with our patients in decisions about their care and futures.
“It affirms that it is for doctors, not judges, to decide on the capacity of under-16s to consent to medical treatment.
“We recognise the work we do is complex and, working with our partners, we are committed to continue to improve the quality of care and decision-making for our patients and to strengthen the evidence base in this developing area of care.”