Puberty blockers have been shown to cause long-term fertility problems in boys, according to a preprint study from Mayo Clinic.
The study, which has not yet been peer-reviewed, analyzed more than 130,000 sperm cells from male children with gender dysphoria.
All participants were 17 or younger.
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The researchers analyzed the testicular cells of boys who had been taking puberty blockers for anywhere from three months to 52 months, and compared them to cells of a control group who had not been on the blockers.
Among those on puberty blockers, the researchers identified mild to severe "sex gland atrophy," determining that the medications accelerated the aging and function of testicular cells.
The findings suggest that puberty blockers’ impacts may be permanent — disputing claims that such effects can be reversed.
The researchers also detected cases of microlithiasis, which is marked by the presence of small clusters of calcium in the testicles.
Additional research from Mayo Clinic has linked testicular microlithiasis to an increased risk of testicular cancer.
"We provide unprecedented histological evidence revealing detrimental pediatric testicular sex gland responses to [puberty blockers]," the authors wrote in the study findings.
Dr. Marc Siegel, clinical professor of medicine at NYU Langone Medical Center and a Fox News medical contributor, was not involved in the Mayo Clinic research but commented on the use of puberty blockers.
"Thousands of U.S. children — more than ever before — are experiencing gender dysphoria and many go on to identify as transgender," Siegel told Fox News Digital.
"They certainly still face a stigma for this, which needs to be addressed — but at the same time, the growing rush to gender-affirming treatment is disturbing, particularly without parental approval."
In 2021, approximately 42,167 children received gender dysphoria diagnoses, almost triple the 15,172 reported in 2017, according to Reuters.
"Much of this is politically driven, and may lead to premature treatments that are not offered in the U.K., Finland, Sweden or many other countries," Siegel said.
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Among the puberty-blocking drugs is lupron (leuprolide), which is a type of hormone therapy used for advanced prostate cancer.
It is also used to stop early puberty in children, according to WebMD.
"It helps to delay sexual development (such as growth of the breasts/testicles) and the start of menstrual periods," WebMD reported.
"It also helps slow down early bone growth to increase the likelihood of reaching normal adult height."
The U.S. Food and Drug Administration (FDA) reported 10,000 adverse effects in children in 2017 — including mood swings, cognitive problems, suicidal thoughts, longer-term fertility problems, seizures, migraines, brittle bones, brain swelling and vision loss, according to Siegel.
Experts also warn of the potential mental impacts of these drugs.
"Transgender individuals are three times more likely than the general population to suffer from anxiety, depression and neurodevelopmental issues," Siegel warned.
Although some studies have shown that interventions such as puberty blockers may decrease anxiety in the short term, Siegel pointed out that "there are no longer-term head-to-head trials versus extensive therapy and watchful waiting."
Puberty blockers typically lead children down a path to long-term use of transgender-affirming hormones, such as estrogen and testosterone, he noted.
"These hormones carry their own risks — for example, estrogen may increase the incidence of breast cancer," Siegel said.
"Bottom line, I don't believe puberty blockers should be given routinely to children and teens for gender dysphoria," Siegel said. "There are too many long-term risks, including the idea that the children or teens may change their minds."
In the majority of cases, Siegel recommends that any hormonal interventions or gender reassignment surgeries be delayed until an older age.
He added, "Intensive supportive and cognitive therapy makes sense as an initial approach."
Dr. Brett Osborn, a Florida neurologist and longevity expert who was also not involved in the new research, noted that previous studies have shown that puberty-blocking drugs can alter the normal progression of testicular cells, potentially leading to atrophy or abnormal development.
"Specifically, the drugs impact the normal function of ‘spermatogonial’ stem cells (SSCs), which are crucial for sperm production and overall reproductive health," he told Fox News Digital.
"Disruption in their development could result in reduced fertility or other reproductive issues later in life," he continued. "Based on the researchers’ histologic findings, the changes induced by these medications may be permanent, contrary to popular opinion among transgender activists."
Added Osborn, "These medications are not as benign as billed."
The risks go beyond infertility, the doctor warned.
"There are also downrange effects of altered hormone levels on brain development, let alone other organ systems," he said.
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Hormones such as testosterone, progesterone and estrogen are critical for brain development, memory and cognition, Osborn pointed out.
The doctor called for "safer and more effective" treatments for those with gender dysphoria.
"Gaining insight into the full impact of these medications — the usage of which has become more prevalent — is crucial for future generations."