May 1, 2021

The Effect of Puberty Blockers on the Accrual of Bone Mass

After two years, up to a third of children have abnormally low bone density

Suppressing puberty in children suffering from gender dysphoria — by administering Gonadotropin-Releasing Hormone agonist (GnRHa) — entails several known risks. One is that patients could “end with a decreased bone density, which is associated with a high risk of osteoporosis” (Delemarre-van de Waal & Cohen-Kettenis 2006).

Bone density was one of the outcomes tracked by the English experiment with GnRHa on children between the ages of 12 and 15, launched by the Tavistock clinic in 2011. As the endocrinologists Dr William J. Malone (an adviser to SEGM) and Dr Michael Laidlaw have pointed out, the published results (Joseph, Ting, & Butler 2019) showed that children experienced a significant decline in bone density relative to the norm for their sex and age—as measured by Z-scores. The study tabulated only the mean and the standard deviation of the Z-scores, and so the proportion of children with Z-scores in the abnormal range was unknown. The threshold of clinical concern is a Z-score below -2. Only 2% of the population would have such low bone density. Indeed, the British experiment included children with a Z-score below this threshold only if they understood the “risks of later osteoporosis.”

Dr Michael Biggs (an advisor to SEGM) has been calling for the release of data from the Tavistock’s experiment since 2019. A subset of the data were finally released following the judicial review into puberty suppression at the Tavistock clinic. Biggs’ reanalysis has just been published in the Journal of Paediatric Endocrinology and Metabolism. It finds that after two years on GnRHa, the Z-scores for a significant minority of the children had declined to a level that should trigger clinical concern. For the hip, one third of Z-scores were below -2. For the spine, over a quarter of Z-scores were below the threshold of -2. Some had even fallen below ‑3; such low bone density is found in only 0.13% of the population.

Bone density after 24 months of puberty suppression

The clinical consequences of the failure to accrue normal bone mass are unknown, because the Tavistock’s researchers have not collected data on fractures experienced by children undergoing puberty suppression. Biggs cites an example of one patient at the Tavistock clinic who started GnRHa at age 12 and then experienced four broken bones by the age of 16. But there is no way of knowing whether this case is exceptional. Researchers in the Netherlands have published similar results on bone density, and likewise have apparently collected no data on fractures. Their latest article suggests that future studies should “investigate clinically important outcomes such as fracture risk” (Schagen et al. 2020).

It is SEGM’s position that clinicians who use GnRHa off-label to must monitor their patients’ bone density and record fractures during puberty suppression. Research must also be undertaken on these patients as they become adults, to see whether the expected higher risk of osteoporosis eventuates.


The full text of the study is available here.