Protesters gathered in August 2021 outside the office of the Prime Minister demanding an end to discrimination against the trans community in the United Kingdom.Vuk Valcic / ZUMA
Last month, the UK’s four-year-long review of medical interventions for transgender youth was published. The Cass Review, named after Hilary Cass, a retired pediatrician appointed by the National Health Service to lead the effort, found that “there is not a reliable evidence base” for gender-affirming medicine. As a result, the report concludes, trans minors should generally not be able to access hormone blockers or hormone replacement therapy (HRT) and instead should seek psychotherapy. While the review does not ban trans medical care, it comes concurrently with the NHS heavily restricting puberty blockers for trans youth.
The conclusions of the Cass Review differ from mainstream standards of care in the United States, which recommend medical interventions like blockers and HRT under certain circumstances and are informed by dozens of studies and backed by leading medical associations. The Cass Review won’t have an immediate impact on how gender medicine is practiced in the United States, but both Europe’s “gender critical” movement and the anti-trans movement here in the US cited the report as a win, claiming it is the proof they need to limit medical care for trans youth globally. Notable anti-trans group the Society for Evidence Based Gender Medicine called the report “a historic document the significance of which cannot be overstated,” and argued that “it now appears indisputable that the arc of history has bent in the direction of reversal of gender-affirming care worldwide.”
Most media coverage of the report has been positive. But by and large that coverage has failed to examine extensive critiques from experts in the US and elsewhere. Research and clinical experts I interviewed explained that the Cass Review has several shortcomings that call into question many of its findings, especially around the quality of research on gender medicine. They also question the credibility and bias underpinning the review. I spoke with four clinical and research experts in pediatric medicine for gender-diverse youth to dive into the criticisms.
“I urge readers of the Cass Review to exercise caution,” said Dr. Jack Turban, director of the gender psychiatry program at the University of California, San Francisco and author of the forthcoming book Free to Be: Understanding Kids & Gender Identity.
The Cass Report’s bar for evaluating research is too high
In scientific research, the randomized control trial (RCT) is often considered the gold standard. In a randomized control trial, study subjects are randomly split up into two groups. One group gets the treatment being examined. The other group doesn’t, and is used as a baseline with which compare the effects of the treatment.
But there are ethical limits to this setup, says Dr. Meredithe McNamara, a professor of pediatrics at Yale School of Medicine who co-leads the Integrity Project, a Yale research hub meant to bridge the gap between policy and science. RCT’s are great when “it is not known whether or not the intervention might be beneficial,” McNamara says. “Having pre-knowledge of benefits means that we would never consider randomizing somebody to no treatment.” In other words, RCTs are a great option when there is not a lot of data pointing to the efficacy of a certain drug or treatment program. But when that data does exist, using RCTS would be considered “unethical” and “coercive,” says McNamara.
In the case of gender-affirming care, decades of research exists showing “gender-affirming care confers key benefits to those who desire and qualify for this care, including youth,” McNamara explains. “It would not make sense ethically to conduct a randomized control trial.” The Federal Drug Administration suggested as much last year, when it told researchers conducting a study on estrogen for trans patients not to use an RCT. That clinical study may include youth as young as 13, per suggestion from the FDA.
The evidence supporting medical interventions for trans youth comes from primarily observational studies, meaning those conducting the research collected data on people undergoing gender-affirming medical care. These kinds of studies are used 70 percent of the time in research on health care, McNamara explains. Alex Keuroghlian, an associate professor of psychiatry at Harvard Medical School and a clinic psychiatrist and director of education at Fenway Health in Boston, emphasizes that gender-medicine providers are not making choices arbitrarily or without robust research. “It’s really setting a double standard in terms of expectations for evidence supporting medical intervention. It is not the standard we expect in other contexts,” they say.
Cass’ systematic evidence reviews used the “somewhat subjective”—as Turban puts it—Newcastle-Ottawa scale rating system to evaluate research on gender-affirming care, which is a rating system to evaluate observational studies. (More precisely, the review actually commissioned researchers at the University of York to conduct the ratings, which Cass then discusses at length in her own report).
The reviewers from York evaluated the research on a scale from “low quality” to “high quality” and found that “much of the research rated as moderate or even sometimes high quality,” explains Turban. But the Cass Review diverged from these findings. Some experts suspect that may be because she compared the research to RCTs despite their inappropriateness. There is “actually wider understanding of the evidence than the Cass Review presents,” says Streed. Cass categorically denies that the review “set a higher bar for evidence than would normally be expected.”
“It’s a bad faith claim that we don’t have enough evidence for pubertal suppressants or gender-affirming hormones,” says Keuroghlian, who has worked with over 2,000 trans and gender-diverse patients in their career. “Gender-affirming medical interventions have been used for adolescent gender dysphoria for decades, and we have a large body of evidence linking them to improved mental health outcomes,” says Turban.
Cass doesn’t apply important terminology consistently or accurately
Multiple experts told me that the language in the review diverged from technical standards and may confuse readers. McNamara explains: “There is a lot of terminology-switching throughout the report.” “Low-quality evidence” is a technical term with specific technical meanings that can be interpreted by researchers, she says. “Weak” or “poor quality,” on the other hand, are “subjective terms that might strike a chord with the lay public but don’t have any concrete meaning.” This means that a reader who is not an expert in medical research may assume that the there are dangers or uncertainties around this health care when there are not.
Perhaps because of the loose use of terminology, the Cass report describes some gender-medicine research as “poor” even though those same studies were rated “moderate” or “high quality” by reviewers at the University of York. The studies downgraded by Cass all demonstrated the efficacy of gender-affirming medical interventions. On the other hand, other studies that didn’t come to such strong conclusions in favor of intervention were not similarly downgraded.
Carl Streed, the research lead for the GenderCare Center at Boston Medical Center and president of the US Professional Association for Transgender Health, clarifies that just because a study is classified as “low-quality” in the report does not mean the data is not robust or rigorous. “It doesn’t actually mean the evidence itself is not to be trusted,” he explains. “It is just that you have to understand the nuance of the methods to understand the context of the results.”
Cass endorses questionable therapeutic treatment
The Cass review recommends psychotherapy as the main and frontline treatment for gender-diverse youth, in place of medical interventions like puberty blockers. But the experts I spoke to say the evidence shows psychotherapy alone doesn’t do enough. Clinicians have been trying “psychotherapy as the way to solve issues around gender since at least the late 1800s” explains Streed. “It wasn’t working. It wasn’t leading to any kind of significant success, people still had significant distress.”
“No contemporary evidence whatsoever shows that people who receive only psychotherapy experience improvements in gender dysphoria,” says McNamara. “There is an abundance of evidence showing that medically affirming interventions confer key benefits and there is none regarding psychotherapy alone.”
What’s more, the therapeutic approach Cass seems to suggests has close ties to conversion therapy. While Cass does not recommend a specific modality, she repeatedly advocates for an “exploratory” approach. She writes: “The intent of psychological intervention is not to change the person’s perception of who they are but to work with them to explore their concerns and experiences and to help alleviate distress.”
Fair enough. Except that these are the same talking points that conversion therapists use to describe their work. There’s even a group, Therapy First, devoted to pushing the idea of “gender exploratory therapy.” Therapy First’s co-founder has advocated to make conversion therapy bans more lenient to make room for an “exploratory” approach. The US Substance Abuse and Mental Health Services Administration has stated that gender change efforts are often “misleadingly referred to as ‘exploratory therapy.’”
Streed explains that “at best, gender exploratory therapy is just delaying people’s access to the care they need, and at worst, it is conversion therapy. That is what we’ve seen in multiple studies, and it is associated with harm.” Keuroghlian puts it more bluntly: “Not providing gender affirming care in a timely way” is “trafficking in conversion efforts.”
“It feels like a double standard to say, ‘Oh, there’s no evidence for medical and surgical interventions with regards to gender-affirming care or affirmation,’ but then, ‘Oh, let’s turn around and offer this other therapy that has absolutely no evidence,’” says Streed.
In a follow-up Q&A, Cass said she “believes that no LGBTQ+ group should be subjected to conversion practice.” At the same time, she stands behind her inclusion of exploratory therapies, saying, “young people with gender dysphoria may have a range of complex psychosocial challenges and/or mental health problems impacting on their gender-related distress. Exploration of these issues is essential.”
The Cass Report shows signs of bias
Cass does a fair amount of work at the outset of the report to make clear that she’s not attempting to undermine “the validity of trans identities” or rollback “people’s rights to healthcare.”
But Cass goes too far in her attempts to remain neutral. The review cites sources that lack credibility or are from anti-trans actors, including an article written a college undergraduate, a pamphlet funded by an anti-trans group, and a YouTube channel run by right-wing commentators. More than once she cites notable exploratory therapists like Ken Zucker.
Further, experts note the report does not disclose all the people who collaborated on the project and their affiliations. Streed says, for similar reviews, “every author has to have their name on it and say what their conflicts of interests are, where they are getting their funding from. The Cass Report does not offer that information. For me, that is a big red flag.” Some of those connections have become clearer since the report was published. For example, the blog Growing Up Transgender uncovered a 2022 meeting between the US Department of Health and Human Services and the Society for Evidence-Based Gender Medicine, which the Southern Poverty Law Center has dubbed “the hub” of the “anti-LGBT pseudoscience network.” Representing SEGM were Richard Byng and R. Stephens, who were identified in the meeting as part of NHS’ “working group on Gender Dysphoria.”
More broadly, Keuroghlian and McNamara both argue that Cass’ conclusions undermining the observational studies is itself a form of bias. “The review’s conclusions are discriminatory,” says Keuroghlian. “It’s an intentional misapplication of science to deny a minoritized group access to medically necessary evidence-based care.” “Any deviation from basic principles of evidence-based medicine suggests bias,” says McNamara.
Allegations of bias in the report are not new. In November 2023, Zinnia Jones, who runs the website and web series Gender Analysis, surfaced court documents in GLAD’s constitutional challenge to Florida’s ban on gender-affirming care for youth. The documentation showed that in 2022, Cass met with Patrick Hunter, a DeSantis appointee to the Florida Board of Medicine, member of SEGM, and big proponent of banning gender affirming medical care for transgender youth.
Hunter sent Cass materials from Florida’s thoroughly discredited 2022 review of gender medicine. That review had gotten edits from Andre Van Mol, a member of a fringe, conservative doctors group that calls itself the American College of Pediatricians (ACPeds). (Read more about Van Mol and his partners in my colleague Madison Pauly’s investigation.) Cass passed along research from her in-progress review and was even invited to do a presentation in front of the Florida Board of Medicine, which was then putting together specific regulations on youth access to HRT and puberty blockers. The Florida review and Cass reports draw similar conclusions about the “weak” research on gender-affirming care.
The experts I spoke to hope the report is not set in stone. “This report and its systematic reviews were just released, and experts are actively reviewing their contents,” Turban says. “Our team has already identified an error with the systematic review on gender-affirming hormones and has notified the journal, requesting a correction be issued.”
“There are no neutral decisions to be made for transgender youth.” McNamara explains, “We have to recognize that physical change that does not align with a person’s gender identity is a source of harm for people who experience gender diversity and dysphoria. Simply watching that happen, feel feels like doing harm.”
Correction: An earlier version of this story misstated the relationship between the Newcastle-Ottawa scale and RCTs.
