Chew et al, 2018


The authors review and summarise the medical literature on suppressing puberty with puberty blockers and cross-sex hormones in gender dysphoric young people. They focus their efforts on studies examining physical, psychosocial and cognitive effects.


The authors find 13 studies that met their inclusion criteria. Nine of these studies examined the effects of blockers. Of these, four examined physical effects, three psychosocial effects, and two cognitive effects.

The studies examining psychosocial and cognitive effects are listed below in Table 1. and summarised at the linked articles. We will update Fully Informed with a review of the studies examining the physical effects at a later date.

The authors assessed the studies risk of bias across three domains using a modified version of the Quality In Prognosis Studies (QUIPS) tool :
  1. Study participation (the study group represents the population of interest).
  2. Study attrition (whether some participants dropped out of the study and remaining participants reflect a potentially biased subsample).
  3. Outcome measures (researchers measured outcomes in a similar way for all participants).

The authors rated each study as having a Low, Medium, or High degree of bias in the three domains.

Table 1. Risk of bias and sample size
Study Measure n Participation Attrition Outcome
Vries et al., 2011¹ Psychosocial 70 High Bias High Bias Medium Bias
Vries et al., 2014¹ Psychosocial 55 High Bias High Bias Medium Bias
Costa et al., 2015² Psychosocial 201 Medium Bias Medium Bias Medium Bias
Staphorsius et al., 2014 Cognitive 116 Medium Bias High Bias Medium Bias
Burke et al., 2014 Cognitive 62 Medium Bias Medium Bias Medium Bias

The authors rated all of the psychosocial and cognitive studies as “Medium” or “High” degree of bias. Vries et al., 2014 has a high degree of bias in two of the three domains. Subsequently, the authors conclude that:

evidence regarding [hormonal treatments’] psychosocial and cognitive impact are generally lacking.

Compare this assessment to the wording in the New Zealand Guidelines used to report the evidence and describe the Vries et al. (2014) study (emphasis added).

There is good evidence that puberty blocking and gender affirming care for trans young people significantly improves mental health and wellbeing outcomes.


There are no high-quality studies on the cognitive and psychosocial outcomes of puberty suppression. Existing studies are few, small scale, with at least moderate degrees of bias. The paper on psychosocial outcomes with the least bias - Costa et al. (2015) - does not show significant outcomes between the treated and untreated groups.

When study authors use standardised evidence quality assessment tools, they report the evidence as weak and generally lacking³. When clinical practitioners make up the majority of a guideline author group - such as in the case of the New Zealand Guidelines - they can misrepresent the evidence (Lenzer et al., 2013).

Doctors prescribing puberty blockers must inform parents that the treatment is experimental and evidence of good outcomes is lacking.