Kinnon MacKinnon, a Canadian researcher, was only faintly surprised this spring when the website for an upcoming conference did not list his talk alongside the dozens of others. He was slated to discuss one of the most fraught topics in medicine: patients who transition to a different gender but later change their minds, known as detransition.

The Pediatric Endocrine Society, which organized the conference, said that his presentation was kept under wraps because of safety concerns; there had been protests against gender medicine at the previous year’s gathering. When he gave the talk in a Chicago hotel ballroom, the audience was asked to submit questions anonymously, on notecards. No recording was allowed. The room, though full, was eerily quiet.

Dr. MacKinnon, a 39-year-old assistant professor of social work at York University in Toronto, is transgender, and he presented alongside another trans researcher. As he took the microphone, he joked: “They really get the trans people in to talk about the easy topics, eh?”

He’s gotten used to trying to defuse tension — at scientific meetings and gender clinics, and in TikTok posts — as detransition, a once-obscure topic, has vaulted into the U.S. presidential campaign and an upcoming Supreme Court case.

A small group of detransitioners — mostly young women who underwent medical treatment to live as trans men, but later regretted it — have become the public faces of Republican-led bans on gender medicine for minors. In frequent testimonies in statehouses and appearances in right-wing media, they have described sometimes irreversible procedures they received while adolescents, arguing that they were misled or neglected by their doctors.

Activists defending youth gender medicine have argued that such experiences are exceedingly rare, and that patients are much less likely to regret their transitions than to regret common medical procedures, like knee surgeries.