Young transgender people are being let down by the "terrible" quality of evidence underpinning their treatment and care, a leading researcher warns.
Prof Carl Heneghan, from Oxford University, said there was an "urgent" need for a new regulator in the field.
He said much more "rigorous" and "robust" research was needed into the effects of drugs given to young transgender people.
But the Department of Health says it has no plans to create a new regulator.
Prof Heneghan, director of the Centre of Evidence Based Medicine at Oxford University, along with Prof Tom Jefferson, who is also a clinical epidemiologist carried out an independent analysis of the most recent international research on medical interventions for the BBC's Panorama programme.
Prof Heneghan said "One of the key issues is to be able to say to parents and children in making a decision... 'Here's an informed decision based on the evidence.'
"The quality of evidence in this area is terrible."
One of the key elements of treatment is puberty blockers, which may be prescribed to young people with gender dysphoria.
They prevent the development of characteristics such as breasts or facial hair.
Puberty blockers have long been used to treat young children who start puberty too early but less is known about their long-term safety in transgender adolescents.
Prof Heneghan said: "What can you tell from the evidence? You can tell very little apart from they give you the intended effects of suppressing and blocking puberty."
Dr Polly Carmichael, a consultant clinical psychologist and director of the NHS Gender Identity Development Service, at the Tavistock Centre, said: "There are questions around risk.
"What you have is a phenomenon and that phenomenon is young people who are hugely distressed around their gender identity.
"I think that it is important that young people and families who have gone forward for treatment are exceedingly positive about it."
'It helps to take time'
Now 18, Jade, was referred to child mental health services for depression in her early teens. Realising that she was conflicted about her gender identity, they referred her on to the Tavistock Centre.
She spent a year on the waiting list, before starting counselling when she was 16-years-old.
"I took a lot of time playing with my identity, which I think is an important thing to do, especially for young people, because it gave me that time to realise that I lived my life as a feminine guy but that wasn't it. There was something more to it," she says.
"When people see me on the street, I want to be perceived as a woman."
Jade, like most under-18s referred to the Tavistock, didn't take puberty blockers or cross-sex hormones while she was a patient there.
"There's just so much thinking that needs to be done, especially to making life changes to go down the line like hormone blockers, when there are so many changes happening in your body," she says.
"It just helps to take time."
Jade says she's still struggling with gender dysphoria but is now ready for the next stage in her transition.
When children have been on puberty blockers for a year, and are about 16, they can be offered cross-sex hormones by the NHS - testosterone and oestrogen, the effects of which can be irreversible.
Prof Heneghan said the way the research studies had collected and analysed evidence "prevented definitive conclusions" to be made on young people's outcomes with cross-sex hormones.
He said the number of patients in the research groups was small and many patients were "lost" from the studies, so their outcomes were not followed up.
The Tavistock Centre has undertaken its own research into patients but he said they had not done enough.
"They haven't produced systematic data on the outcomes based on all children," Prof Heneghan said.
"In the absence of evidence, I just do not understand how they can inform children, adolescents and parents and families in a way that helps them make an informed decision."
However, Dr Carmichael said the centre had recently been given a research grant "to follow young people who come to the service through and forward, whatever their outcomes, and that is going to be really important information".
The Tavistock Centre also said it engaged in research and published regularly.
But Prof Heneghan said a new regulator was urgently needed to provide oversight of the care and treatment offered by both the NHS and private providers.
He likened the "emotive" area of care for transgender children to that for fertility and called for a new regulator to oversee research and treatment, similar to the Human Fertilisation and Embryology Authority (HFEA), which would be independent to those providing the care.
The Department of Health said it had no plans to introduce an independent regulator but added: "We are committed to ensuring thorough accountability and oversight... and will review any arrangements when appropriate."
Panorama: Trans Kids - Why Medicine Matters is available on BBC iPlayer.
Dr Faye Kirkland is also a GP.