Puberty blockers: what they are, how they work, and what science says

Puberty blockers are among the most debated — and most misunderstood — topics in the discussion on transgender health. They are discussed in legislatures, on talk shows, and on social media, often in polarized terms: some describe them as a life-saving intervention, others as a dangerous experiment on minors. The scientific reality is more nuanced than either of these narratives. In this article, we examine what these medications are, how they work, what the research says about their benefits and risks, and what the regulatory situation looks like internationally, with specific references to the medical literature.

What they are and how they work

Puberty blockers are medications belonging to the class of GnRH agonists (gonadotropin-releasing hormone). The most commonly used active ingredient is triptorelin, marketed under names such as Decapeptyl and Gonapeptyl. These medications act on the hypothalamic-pituitary-gonadal axis: when administered continuously, they saturate the GnRH receptors in the pituitary gland, initially causing a brief stimulation followed by a desensitization that blocks the release of LH and FSH. The result is the suppression of estrogen or testosterone production by the gonads and, consequently, the cessation of pubertal development [1][14].

In practical terms, the development of secondary sex characteristics — breast growth, voice changes, body fat distribution, hair growth — stops. Development is not reversed: changes that have already occurred remain, but do not progress further.

Treatment is administered via intramuscular or subcutaneous injection, with extended-release formulations (monthly or quarterly). Administration occurs under specialist medical supervision.

History of clinical use

GnRH agonists are not new medications. They have been used in pediatrics since 1981 for the treatment of central precocious puberty — a condition in which pubertal development begins before ages 7-8 in females or 9 in males. In this context, triptorelin and similar molecules have been prescribed for over forty years and are considered safe and effective, without consistently documented serious long-term adverse effects [14].

Their application to gender dysphoria in minors is more recent. The first structured protocol was developed in the Netherlands in the 1990s at the VU University Medical Center in Amsterdam. Known as the “Dutch protocol,” it involved pubertal suppression beginning at Tanner stage 2 (the first physical signs of puberty), followed by cross-sex hormone therapy around age 16 and, in adulthood, possible surgical interventions. This three-phase model was the starting point for the major international guidelines [4][13].

The first prospective study on the Dutch protocol outcomes was published in 2011 by de Vries and colleagues, documenting improvements in psychological functioning among adolescents after pubertal suppression [13]. The most cited study by the same group, published in 2014 in Pediatrics, followed 55 young transgender adults from the start of pubertal suppression through post-surgical outcomes, showing progressive improvement in psychological well-being [4].

Who are they indicated for

Puberty blockers for gender dysphoria are not prescribed to prepubertal children. The major guidelines agree on this point: treatment is indicated only after the onset of puberty, typically starting at Tanner stage 2 (the first visible stage of pubertal development) [1][2].

The Endocrine Society guidelines (2017) recommend pubertal suppression with GnRH agonists for adolescents who have reached Tanner stage G2/B2, with a confirmed and persistent diagnosis of gender dysphoria [1]. The same guidelines expressly recommend against hormonal treatment of prepubertal children.

The WPATH SOC-8 (2022) confirms the indication for pubertal suppression when appropriate, emphasizing an individualized approach rather than rigid age thresholds [2]. It requires a comprehensive biopsychosocial assessment by mental health professionals to understand the individual characteristics, vulnerabilities, and diagnostic profile of the adolescent.

Reversibility

One of the central aspects of the debate is the reversibility of treatment. The major international guidelines classify pubertal suppression as a reversible intervention: upon discontinuation of the medication, endogenous puberty resumes its course [1][2][14].

This is a crucial point that distinguishes blockers from hormone therapy with estrogen or testosterone, which produces partially permanent changes (such as voice deepening in the case of testosterone, or breast development in the case of estrogen). Pubertal suppression, in this sense, was conceived as a “pause” to give the adolescent — and the clinical team — time to carefully assess the most appropriate path, without the pressure of irreversible physical changes in progress.

In clinical practice, a significant proportion of adolescents who begin pubertal suppression subsequently proceed to cross-sex hormone therapy. This finding has been interpreted in opposing ways: by some as evidence that treatment works as an appropriate filter, by others as an indication that pubertal suppression may consolidate an identity that might otherwise have evolved. The 2024 Cass Review emphasized that the available data do not allow distinguishing between these two interpretations [9].

It should also be noted that, while puberty resumes upon discontinuation, the long-term effects of prolonged suppression on certain parameters — such as bone density and future fertility in the case of direct transition to cross-sex hormones without gametic maturation — remain under study.

Documented benefits

Research on the psychological outcomes of pubertal suppression shows generally positive results, although with methodological limitations that are important to acknowledge.

The de Vries et al. (2014) study, conducted on 55 young transgender adults (22 trans women and 33 trans men), followed participants from initial pubertal suppression (mean age 13.6 years) through hormone therapy (mean age 16.7 years) to post-surgical outcomes (mean age 20.7 years). Results showed that gender dysphoria had been alleviated and psychological functioning had improved progressively, reaching levels comparable to those of the general Dutch population [4]. This is a foundational study but with a small sample and no control group.

The Turban et al. (2020) study, published in Pediatrics, analyzed data from the 2015 U.S. Transgender Survey. Of 20,619 transgender adults aged 18 to 36, 3,494 (16.9%) had desired pubertal suppression during adolescence, but only 89 (2.5%) had actually received it. Those who had received treatment showed a 70% reduction in lifetime odds of suicidal ideation (OR 0.3; 95% CI 0.2-0.6) [5]. The study has significant limitations: the sample of those who received blockers was very small (89 individuals), the design is retrospective and cross-sectional, and it is not possible to rule out that adolescents with more severe psychological problems were less eligible for treatment in the first place.

The Tordoff et al. (2022) study, published in JAMA Network Open, followed 104 transgender and nonbinary youth (ages 13-20) for 12 months. Those who received puberty blockers or gender-affirming hormones showed a 60% reduction in odds of moderate or severe depression and a 73% reduction in odds of suicidal ideation [6]. Again, this is a prospective observational study without randomization.

Overall, the available literature suggests an association between pubertal suppression and improvement in mental health outcomes, but the quality of the evidence — as acknowledged by the scientific community itself — remains moderate, with predominantly observational studies, small samples, and absence of randomized controlled trials.

Side effects and areas of research

An honest approach to the topic of blockers requires carefully examining both the benefits and the risks and areas where knowledge is still incomplete.

Bone mineral density

The effect on bone density is the most well-documented risk. Puberty is a critical period for bone mass accumulation, and suppression of sex hormones interferes with this process. Several studies show a reduction in bone mineral density z-scores during treatment with GnRH agonists [7][8].

The Joseph et al. (2019) study, conducted on 70 adolescents (ages 12-14), found a significant reduction in BMD z-scores at the hip and lumbar spine after one year of treatment [8].

The van der Loos et al. (2023) study, published in JAMA Pediatrics, examined 75 transgender participants with a median follow-up of over 11 years. Results show a differentiated picture by sex assigned at birth: in trans men (assigned female at birth) treated with testosterone, bone density tended to recover, reaching levels close to baseline. In trans women (assigned male at birth) treated with estrogen, lumbar spine z-scores remained significantly reduced (-1.34), suggesting incomplete recovery [7].

Guidelines recommend periodic bone density monitoring, calcium and vitamin D supplementation, and physical exercise throughout the period of suppression [1].

Fertility

An area of uncertainty concerns fertility. If pubertal suppression is followed directly by cross-sex hormone therapy without endogenous puberty having achieved sufficient gametic maturation, future reproductive capacity could be compromised. The Endocrine Society guidelines recommend that all adolescents and their families receive information about fertility preservation before beginning treatment [1]. However, concrete preservation options (cryopreservation of oocytes or sperm) can be limited in adolescents at early pubertal stages.

Brain development

The potential effects on cognitive and brain development represent an area where data are particularly scarce. Puberty is associated with important brain maturation processes, and the 2024 Cass Review highlighted the lack of sufficient data to assess the impact of pubertal suppression on these processes [9]. This is not a statement of harm, but an acknowledgment of uncertainty that requires further research.

Psychological and cognitive effects

Some studies report possible effects on mood during treatment, but the data are inconsistent. It is difficult to separate the effects of the medication from the psychological impact of the condition itself and the social context in which the adolescent lives. Regarding cognitive development, the Cass Review (2024) noted that available data are insufficient to assess with certainty the impact of pubertal suppression on brain maturation [9]. This is an area where research is still in its early stages: there is no definitive evidence of cognitive harm, but neither are there sufficient data to rule it out, making further longitudinal studies necessary.

Rate of progression to hormone therapy

A frequently cited figure in the debate concerns the percentage of adolescents who, after starting pubertal suppression, proceed to cross-sex hormone therapy. Several studies report rates between 95% and 98%. This finding has been interpreted in opposing ways: as confirmation that blockers are prescribed to adolescents with genuinely persistent dysphoria, or as an indication that pubertal suppression may consolidate a path that not all would have otherwise taken. The Cass Review of 2024 emphasized that the available data do not allow distinguishing between these two interpretations, and that the absence of an adequate control group makes it impossible to determine whether treatment influences the subsequent decision [9]. This ambiguity is one of the main arguments in favor of controlled clinical trials.

The international debate

The international landscape on pubertal suppression for gender dysphoria has undergone significant changes in recent years, with positions that are not uniform.

The Cass Review (United Kingdom, 2024)

The Cass Review, commissioned by NHS England and conducted by pediatrician Hilary Cass, was published on April 10, 2024 after four years of work. The final report concluded that the evidence supporting medical interventions (both blockers and hormones) for minors with gender dysphoria is “disappointingly scarce” [9].

In particular, the systematic review conducted by the University of York found that the results of the original Dutch study — which showed psychological improvements with blockers — had not been replicated in the study conducted in the United Kingdom (GIDS). The report recommended that puberty blockers be available for transgender adolescents only within the context of formal clinical trials with rigorous standards [9]. NHS England implemented this recommendation.

The Cass Review received both broad endorsement and criticism. Several medical societies welcomed it as a step toward more evidence-based medicine. Other researchers contested the methodology, particularly the criteria used to assess study quality, arguing that similar standards would exclude much of pediatric research in many other fields.

Sweden and Finland

Finland was among the first countries to revise its guidelines. In June 2020, the national council for health and welfare published new recommendations that prioritize psychosocial interventions over medical ones for young people with gender dysphoria, especially in cases of post-pubertal onset.

Sweden followed a similar path. In May 2021, the Karolinska Hospital in Stockholm established that hormonal treatments for minors with gender dysphoria could be provided only in approved research settings. In February 2022, the Socialstyrelsen (national health authority) issued national guidelines reflecting this restrictive approach, concluding that the risks of blockers and cross-sex hormone treatment in minors likely outweigh the expected benefits.

Positions of WPATH, Endocrine Society, and AAP

In contrast to European restrictions, the major international medical organizations continue to support pubertal suppression as an appropriate therapeutic option.

The WPATH SOC-8 (2022) maintains its recommendation for the use of blockers when indicated, with individualized assessment [2]. The Endocrine Society (2017) recommends pubertal suppression starting at Tanner stage 2, confirming this position even after the publication of the Cass Review [1]. The American Academy of Pediatrics (2018) reaffirmed its support for gender-affirming care for minors, including pubertal suppression, reaffirming its policy in 2023 [3].

This divergence between more restrictive European approaches and positions of international medical societies reflects an ongoing scientific debate, not a settled question.

Summary of the international landscape

For orientation in the debate, a concise summary of major national decisions is useful:

• Finland (2020): new guidelines centralize treatment and prioritize psychosocial interventions over pharmacological ones, with more restrictive access criteria than before.
• Sweden (2022): the Socialstyrelsen establishes that blockers and cross-sex hormones for minors can be administered only in approved research settings, after the Karolinska Hospital had already limited access in 2021.
• United Kingdom (2024): the Cass Review recommends formal clinical trials as the only context for prescribing blockers. The NHS suspends routine prescribing and the British government implements an indefinite ban in December 2024.
• International organizations: WPATH, Endocrine Society, and AAP continue to recommend pubertal suppression as an appropriate therapeutic option for selected adolescents.

This landscape shows that there is no uniform international consensus: some European countries have adopted a more cautious approach, while the major medical societies maintain their recommendations in favor of treatment access.

What the guidelines say

A summary of the positions of major medical authorities:

Endocrine Society (2017) — Recommends pubertal suppression with GnRH agonists starting at Tanner stage G2/B2. Expressly recommends against hormonal treatment of prepubertal children. Requires multidisciplinary team and fertility counseling [1].

WPATH SOC-8 (2022) — Supports pubertal suppression and hormone therapy when indicated, with an individualized approach and comprehensive biopsychosocial assessment. Does not set rigid age thresholds but requires high standards of evaluation [2].

AAP (2018, reaffirmed 2023) — Supports the gender-affirming approach, including pubertal suppression from Tanner stage 2 and subsequent cross-sex hormone therapy. Acknowledges uncertainty about long-term effects of prolonged suppression on fertility [3].

Cass Review (2024) — Concludes that the evidence supporting blockers is weak and recommends they be available only within the context of formal clinical trials with rigorous standards [9].

A topic that demands intellectual honesty

The debate on puberty blockers touches profound questions: the protection of minors, the right to health, the autonomy of medical science, the precautionary principle. Reducing it to slogans — “they’re safe” or “they’re dangerous” — does not do justice to the complexity of the evidence.

What the research says with reasonable certainty is that pubertal suppression is a pharmacological intervention with a long history of pediatric use, that the most authoritative international guidelines continue to recommend it as an appropriate option for selected adolescents with persistent gender dysphoria, and that available studies show an association with positive psychological outcomes.

What the research has not yet definitively clarified concerns the long-term effects on bone density (especially in trans women), on fertility in cases of direct transition to cross-sex therapy, and on brain development. The overall quality of the evidence is recognized as moderate, and the need for more robust studies is shared across all positions in the debate.

In a context where decisions concern the lives of real adolescents — with their families, their suffering, and their hopes — the most responsible answer is neither uncritical enthusiasm nor ideological rejection, but rigorous research, transparency about the limits of what we know, and respect for the clinical expertise of those who work daily with these young patients.