A large majority of transgender adolescents who received puberty suppression treatment went on to continue gender-affirming treatment, a new study from the Netherlands has found.

The study, published in The Lancet, used data that included people who visited the gender identity clinic of Amsterdam UMC, a leading medical center in the Dutch capital, for gender dysphoria. (Gender dysphoria refers to psychological distress that results from an incongruence between one's sex assigned at birth and one's gender identity.)

Researchers found that a whopping 98% of people who had started gender-affirming medical treatment in adolescence continued to use gender-affirming hormones at follow-up. The finding is significant because of ongoing political debates over whether young people should receive gender-affirming treatment, with some opponents arguing that many transgender children and teens will realize later in life that they aren't really trans.

The paper's data included people who started medical treatment in adolescence with puberty blockers before the age of 18 for a minimum duration of three months, before adding gender-affirming hormones. Researchers then linked that data to a nationwide prescription registry in the Netherlands to look for a prescription for gender-affirming hormones at follow-up.

The study, thought to be the largest of its kind, provides a new data point in the highly charged political debate over the prescribing of puberty blockers or providing gender-affirming medical care to trans youth. Young people seeking transition-related treatment are sometimes told that they are simply going through "a phase" that they'll grow out of.

Marianne van der Loos, a physician at Amsterdam UMC's Center for Expertise on Gender Dysphoria, is the paper's lead author.

"I think it's an important finding because we see that most of these people continue to use gender-affirming hormones," van der Loos tells NPR.

The debate over whether youths should be able to access gender-affirming care is largely a political one. Major medical organizations in the U.S. have published guidelines for providing appropriate gender-affirming care.

For example, the American Academy of Child and Adolescent Psychiatry has stated that it "supports the use of current evidence-based clinical care with minors. ... Blocking access to timely care has been shown to increase youths' risk for suicidal ideation and other negative mental health outcomes."

The subject of medical treatment for trans adolescents is a hot topic not only in the U.S., but in the Netherlands as well, says van der Loos: "There's just a lot of people having an opinion on this."

The cohort study included 720 people, of whom 31% were assigned male at birth, and 69% were assigned female at birth. The presence of more people assigned female at birth is a reflection of the population who sought gender-affirming treatment at this clinic.

For the 2% of people in the cohort who did not appear to continue treatment with gender-affirming hormones, the researchers were not able to identify the cause.

"We aren't sure that they really quit treatment. We couldn't find a prescription for gender-affirming hormones for those people. So it seems that they don't have one anymore in the Netherlands. And we can't really tell from this data as to why they would have quit," says van der Loos, adding that it's an important question to answer in further research, along with the long-term effects of the treatment protocol on bone health.

Van der Loos emphasizes that mental health support is a key part of the treatment at Amsterdam UMC, with a diagnostic evaluation prior to a patient starting puberty suppression, and continued mental health care during treatment. As a result, van der Loos wasn't surprised to find that most of those who began treatment chose to continue it.

"These were people that were supported by a mental health professional before start of treatment, [and] also after start of treatment. So based on that and our clinical experience, it's not really surprising that so many people continue to treatment later on," she says.

And, van der Loos notes, mental health support may not be a part of treatment everywhere.