Transgender people who start hormones when they are teenagers have far better mental health than if they wait until adulthood, according to new research.
Experts found they had fewer suicidal thoughts, were less likely to experience major mental health disorders, and had fewer problems with substance abuse than those who started hormones in adulthood.
The issue of giving youngsters hormones has proved controversial over the years.
The drugs can only be given in the UK from the age of 16 to those who have been on puberty blockers for at least 12 months.
In general, people wanting masculinisation take the hormone testosterone while people wanting feminisation take oestrogen.
For the new study, led by the Stanford University School of Medicine, data was gathered from the largest survey of US transgender adults – a group of 27,715 people who responded in 2015.
As well as fewer mental health concerns amongst people started hormones as teenagers, the study found that those who took the drugs at any age had better mental health than those who wanted them but never got them.
Of the 21,598 people who wanted hormones or received them, 119 began getting hormones at age 14 or 15 (early adolescence), 362 at age 16 and 17 (late adolescence), and 12,257 after their 18th birthday (adulthood).
Some 8,860, who served as the control group, wanted but never received hormone therapy.
Compared with the control group, people who underwent hormone treatment had lower odds of experiencing severe psychological distress during the previous month and lower odds of suicidal thoughts in the previous year.
Odds of severe psychological distress were reduced by 222%, 153% and 81% for those who began hormones in early adolescence, late adolescence and adulthood respectively.
Odds of feeling suicidal in the previous year were 135% lower in those who began hormones in early adolescence, 62% lower in those who began in late adolescence and 21% lower in those who began as adults, compared with the control group.
Dr Jack Turban, lead author on the study and expert in paediatric and adolescent psychiatry at Stanford Medicine, said: “This study is particularly relevant now because many state legislatures are introducing bills that would outlaw this kind of care for transgender youth.
“We are adding to the evidence base that shows why gender-affirming care is beneficial from a mental health perspective.”
Last September, the UK Court of Appeal overturned a judgment that children under the age of 16 considering gender reassignment were unlikely to be mature enough to give informed consent to be prescribed puberty-blocking drugs.
Tavistock and Portman NHS Foundation Trust, which runs the NHS’ only gender identity development service for children, challenged a high court ruling in a case brought against the service by Keira Bell, a 24-year-old who had begun taking puberty blockers when she was 16.