Mayo Clinic Research: Hormone Blockers Linked to Testes Shrinkage and Fertility Problems, Raises Concerns About Reversibility

Boys who take puberty blockers may suffer atrophied testes and fertility issues, a new study by Mayo Clinic researchers has found, causing the authors to cast doubt about the common claim that puberty blockers are “reversible.”

The study, authored by 11 researchers at Mayo Clinic’s largest campus south of Minneapolis, looked at the effects of puberty blockers on testicular cells and function.

“We provide unprecedented histological evidence revealing detrimental pediatric testicular sex gland responses to [puberty blockers],” the study reads.

Mild to severe sex gland atrophy is one of the negative effects the researchers found.

In the case of one 12-year-old boy who was treated with puberty blockers for 14 months, nearly 60% of his sex glands became “fully atrophied,” and small clusters of calcium formed in his testicles, according to the study.

These calcium clusters are linked to cancer, several studies have found, although it is not clear whether they are a risk factor by themselves.

Potentially permanent effects on fertility were another concern for boys who were treated with puberty blockers, the researchers found.

In the case of a 14-year-old boy who had been puberty blockers for more than four years, more than 90 % of his cells that were supposed to eventually produce sperm were developmentally arrested.

The findings “raise a potential concern regarding the complete ‘reversibility’ and reproductive fitness” of the sperm germ cells, the researchers said.

The study examined 87 boys, 16 of whom were gender dysphoric boys between ages 10 and 16. Nine of those boys were already on puberty blockers, although all of the boys would eventually be put on the drugs. The boys began identifying as transgender girls between ages 2 and 15.

The researchers noted that there are no long-term studies on puberty blockers for gender dysphoric children, meaning many of the drugs’ effects such as impacts on fertility are still unknown.

The study has not yet been peer-reviewed but was published on BioRxiv, a website hosted by the Cold Spring Harbor Laboratory that sees two-thirds of its papers later published in peer-reviewed journals.

Mayo Clinic’s website page on puberty blockers does not yet warn about the extent of the side effects found in the study. The page says the drugs “don’t cause permanent physical changes” and when a child stops taking them, “puberty starts again.”

“[T]hey pause puberty,” the page says. “That offers a chance to explore gender identity. It also gives youth and their families time to plan for the psychological, medical, developmental, social and legal issues that may lie ahead.”