A new study examining the effects of testosterone therapy on transmasculine youth has found that the treatment does not lead to increased anger or irritability after a year. In some cases, researchers even observed a reduction in aggressive behaviours.
The research, published this week in the Journal of Adolescent Health, addresses a common concern among transgender young people and their families that testosterone therapy might cause heightened anger, irritability or aggression.
It also challenges claims made by some anti-trans activists who have suggested that hormone therapy contributes to violent behaviour. These arguments gained attention following a small number of high-profile incidents involving transgender individuals, including the 2023 school shooting at the Covenant School in Nashville.
However, experts note that transgender people account for a very small proportion of perpetrators of mass violence. Gun violence researcher James Densley, co-founder and deputy director of the Gun Violence Archive, said: “Put simply, transgender individuals account for a vanishingly small proportion of perpetrators.”
Research Across Major US Gender Clinics
The study was conducted by nine researchers affiliated with leading children’s hospitals in the United States, including Ann & Robert H. Lurie Children’s Hospital of Chicago, Boston Children’s Hospital and Benioff Children’s Hospital at the University of California, San Francisco.
Researchers followed 178 transgender and gender-diverse adolescents and young adults who began testosterone therapy across four gender care centres in the United States.
Participants were aged 12-20 years, with an average age of 16. The majority, 92 percent, identified as transmasculine or male, and 58 per cent of participants were white. All participants had completed puberty and had not previously used puberty blockers.
Anger Levels Remained Stable
The findings showed that self-reported levels of anger, aggression and irritability were generally within normal ranges when participants began testosterone therapy. Twelve months later, those levels remained largely unchanged.
At the start of the study, around 45.5 per cent of participants reported slightly elevated anger or other externalising behaviours. By the 12-month mark, average levels for this group had dropped into the normal range.
Overall, 69.6 per cent of participants maintained normal anger levels throughout the study period. Another 19.2 per cent moved from elevated anger levels to normal levels after starting treatment, while 11.2 per cent shifted from normal to elevated levels.
Adjustment Period Not Captured
Researchers noted that the study did not specifically track emotional changes during the first few months after starting testosterone therapy. That early adjustment period can involve both physical and mental stress as patients adapt to hormonal changes.
Despite this limitation, the authors said the findings help address widespread concerns about behavioural side effects.
“Despite concerns commonly raised by youth and their families, there is not a clinically significant concern for increased anger, irritability, or aggression as a side effect of testosterone,” the researchers concluded.
They added that transgender adolescent and young adult males showed “levels of anger, irritability, and aggression comparable to normative samples over time as a whole.”
