Supreme Court heard arguments on Tennessee ban on transgender care. What does the science say?

Last year, Tennessee banned doctors from medically slowing down a teenager's puberty or giving them hormones or surgery to alter their gender.

Families of transgender teens in the state sued to protect their right to make their own medical decisions, and now the case is before the U.S. Supreme Court. Oral arguments ended Wednesday and the court is expected to decide by the summer.

The Tennessee law says it has a “compelling interest in encouraging minors to appreciate their sex” and in prohibiting the procedures “that might encourage minors to become disdainful of their sex.”

Tennessee is one of two dozen states that ban what's commonly known as gender-affirming care, so the court's decision could have broad implications.

Gender-affirming care is a range of social, psychological, behavioral and medical interventions designed to support a person in affirming their gender identity, according to the World Health Organization.

The American Medical Association, which represents more than 250,000 U.S. doctors, passed a resolutionlast year calling for protection for this type of care. More than 30 major medical associations and health organizations worldwide support health care for transgender adults and youth, which they say can help prevent suicide in this vulnerable population.

Here's what the science says.

Puberty blockers and hormone therapy

Most patients with gender dysphoria, which is distress due to a mismatch in biological sex and gender identity, have already gone through puberty when they first seek treatment, said Dr. Joshua Safer, an endocrinologist and executive director of the Mount Sinai Center for Transgender Medicine and Surgery in New York. Only a handful are at the beginning stages of puberty.

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In these instances, Safer said, puberty blockers may be used to delay the onset of puberty or pause it in its tracks. These medications, called GnRH agonists, stop the body from making sex hormones, such as testosterone and estrogen.

In people assigned male at birth, such treatment slows down the growth of facial and body hair, prevents voice deepening and limits the growth of sex organs, according to the Mayo Clinic. In people assigned female at birth, it limits breast development and stops menstruation.

Puberty blockers are meant to be taken temporarily because the body needs sex hormones, Safer said. For example, they play a major role in bone growth and development.  

“A year or two is safe and that’s it,” he said. “You can’t show up and be on puberty blockers for 10 years.”

Experts say delaying puberty gives transgender patients more time to explore and integrate their identity before coming off the puberty blockers. When they do, they may proceed to gender-affirming hormone therapy or resume puberty of their sex assigned at birth.

The two-year benchmark is based on safety data among children with precocious puberty, when a child’s sexual development occurs too early, for which the drug was initially approved. One of the arguments before the court is whether it would be legal to block the drug's use for one purpose ‒ precocious puberty ‒ while denying its use for another.

Critics of puberty blockers argue there's not enough research showing that the temporary use of these medications during childhood doesn't have lasting health effects. They also claim there's little data showing puberty blockers lead to beneficial mental health outcomes in transgender youth.

The Cass Review: Transgender care in England

Opponents of gender-affirming care for people under 18 often point to The Cass Review, named after British pediatrician Dr. Hilary Cass, who chaired the review.

The National Health Services England commissioned the investigative report in 2020 to evaluate gender-affirming services in the United Kingdom, citing long waitlists in gender identity clinics due to a stark increase in young adults seeking care.

The final report, published in April 2024, concluded there was a lack of evidence supporting medical interventions like puberty blockers and hormone therapy to manage gender-related distress in teens.

Supreme Court live updates:Latest from oral arguments on transgender care case

Cass recommended these interventions be used only for research purposes, which prompted the NHS England to stop prescribing puberty blockers for transgender adolescents outside of a clinical trial and open new gender centers that take a more "holistic" approach, according to a statement released in August.

Many experts – from the U.S. and countries worldwide – have concerns about the report and the government's response.

Dr. Carl Streed, Jr., president of the U.S. chapter of the World Professional Association for Transgender Health, disagrees with the methodology and findings of the Cass report. It failed to include many studies showing the benefits of puberty blockers and hormone therapy, he said.

More research into transgender youth is always welcomed but disrupting care in the pursuit of more data can have harmful consequences, he said.

"When we ban care or slow down care, we're affecting an entire age cohort and putting them at risk for worse mental health," said Streed, who is also the research lead for the GenderCare Center at Boston Medical Center.

Is the Tennessee ban ‘what’s best for children’?

While the science continues to be debated, opponents of the Tennessee ban say the law has nothing to do with science.

Enacted in 2023, Tennessee’s law bans doctors from giving puberty blockers or hormone therapy to a minor seeking treatment for gender dysphoria.

The state says it has a “compelling interest in encouraging minors to appreciate their sex” and in prohibiting the procedures “that might encourage minors to become disdainful of their sex.”

“The blanket bans of providing evidence-based gender-affirming care reveals that it’s all about politics and not the evidence," Streed said.

Transgender lawyer makes history:Takes case on puberty blockers and hormone therapy to Supreme Court

Steve Sanders, an expert on sexuality and gender identity and law at Indiana University, said the science behind puberty blockers and hormone therapy for transgender youth is "spotty and observational." But the bans in Tennessee and other states are likely not a product of "serious, thoughtful, earnest and profound debate about what's best for children."

"These bans were produced as part of an intentional strategy by social and religious conservatives to demonize and scapegoat transgender people," he said during a panel discussion hosted by The Federalist Society, a group of conservative lawyers.

Dr. Roy Eappen, an endocrinologist with the conservative organization Do No Harm, supports the bans in Tennessee and other states. Although they don't address the crux of the issue, which he argues is the lack of scientific evidence, the bans successfully stop care that he believes could harm minors.

"When doctors don't do their job, it's up to the state to intervene," he said.

Health risks of banning gender-affirming care

There is no routine protocol for gender-affirming care, Safer said. Each treatment plan is individualized to the patient’s needs.

But in general, doctors are cautious when treating transgender youth.

“The approach for young people is conservative,” Safer said. “We try to be thoughtful and conservative when we support parents and kids.”

Despite treating conservatively, doctors who work in transgender care argue children and adolescents who identify as transgender should have these treatments available to them as options.

Like other medications, experts say there are risks associated with taking puberty blockers and hormones. For example, the American Academy of Pediatrics says a child taking puberty blockers could experience stress or lower self-esteem as their peers reach puberty.

However, all the major medical organizations in the U.S. say studies show gender-affirming care for transgender youth leads to better mental health outcomes, including lower odds of depression and suicidality in the short term.

"As a scientist, I will never turn down additional research funding support. Asking for more people to collect data more carefully is not controversial," Safer said. "But the data (supporting gender-affirming care) are quite strong. Denying care is associated with harm, not differently than denying any medical care."