A long-awaited, taxpayer-funded study of transgender-identifying youth found that puberty blockers and cross-sex hormones may carry significant risks to bone density, cardiovascular health, and fertility.
The National Institutes of Health provided up to $10 million for the nine-year study, conducted through Children’s Hospital Los Angeles and led by Dr. Johanna Olson-Kennedy, a prominent provider of so-called “gender-affirming care.”
The study included participants as young as 8. Researchers found that children entering the puberty-blocker group already had lower bone-mineral density than the general population, raising concerns about the potential long-term effects of suppressing normal puberty.
The report also identified cardiovascular risk factors among young people receiving cross-sex hormones. Those taking testosterone experienced decreases in HDL, commonly known as “good” cholesterol, and increases in LDL, or “bad” cholesterol.
Among biological females receiving testosterone, 6.5% developed hematocrit levels above 50%, meaning an abnormally high concentration of red blood cells—a condition that can increase the risk of vascular complications.
Researchers also acknowledged unresolved questions surrounding fertility and reproductive health, establishing a tissue archive to study the long-term effects of these treatments.
The findings come after controversy surrounding the study’s delayed publication. The New York Times reported in 2024 that Olson-Kennedy had withheld some findings because she feared they could be “weaponized” in political debates over transgender medical treatments for minors.
The newly released report also follows findings showing that puberty blockers produced no clinically significant improvement in overall mental health over two years.