Does testosterone therapy affect the brain?

Help! Testosterone Is Melting My Brain! (Maybe.)

Help! Testosterone Is Melting My Brain! (Maybe.)

Expanding the LGBTQ Conversation
Aug. 26 2016 11:28 AM

Help! Testosterone Is Melting My Brain! (Maybe.)



I don’t want to alarm you, reader, but my verbal ability may be deteriorating even as I write this. As part of my medical transition from female to male, I have started testosterone therapy. The latest neurological research indicates that testosterone may literally shrink parts of the brain associated with speech and language processing. This is not cool if you happen to be a professional writer who is also a trans man on hormone replacement therapy, a common predicament I assume most Americans are familiar with.

There’s a lot that’s muddy and inconclusive in the realm of sex-based brain differences, but one of the clearest results from the scientific literature is that men score worse on tests of verbal ability and that testosterone may have something to do with delays or reductions in language (at least in childhood).


It probably shouldn’t have to be said that any differences in verbal ability refer to the statistical averages of the groups, that individual men and women vary much more widely within their respective groups than the groups do from each other, and that there is extensive overlap. A statistical difference between male and female brains with plenty of overlap makes a lot of intuitive sense if you think about more familiar differences between the sexes: Women and men have height differences, as we all know, but individual heights vary widely, and there is significant overlap between normal male and female tallness. A 6-foot-3 woman or a 5-foot-tall man do nothing to challenge our understanding of male and female height differences.

Similarly, the existence of men who write well or studies that show significant overlap between the brains of men and women should not challenge our broad understanding of how innate sex-based cognitive differences work, if they exist. While we should inspect studies of sex-based differences in intellect or emotional makeup carefully for signs of bias, or unaccounted-for factors that could undermine any individual study (or all of them), the likelihood is that men and women’s brains differ to some extent and that sex hormones play a role in how those differences develop.

The role of testosterone in brain-based sex differences is not perfectly understood, but there are intriguing indications that testosterone accounts for at least some of the difference in linguistic proficiency between men and women. One of these indications comes in the form of an Austrian study of transgender men, authored by Andreas Hahn, which looked at the brains of trans men before and after they started testosterone therapy. MRIs conducted on the brains of more than a dozen trans men (and on a control group of cis women) showed that the trans men lost gray matter in two key areas of the brain associated with speech and language, specifically Broca’s and Wernicke’s areas. It was a small study, certainly not one that should be taken as conclusive evidence of anything on its own, but it suggests a possible effect of testosterone that anyone currently taking intramuscular testosterone, or considering it, would want to see more research about.

The Hahn study explicitly concerned itself with the question of how male and female brains differ—and that question exclusively. The paper notes that “ethical considerations mostly limit investigations to single hormone administrations. To circumvent this issue we assessed the influence of continuous high-dose hormone application in adult female-to-male transsexuals.” In other words, ethics precluded researchers from giving females more than a single small dose of testosterone, but with trans men they have a population that is willingly self-administering multiple large doses, enough to bring their testosterone levels into the male range. That’s great news for science, but Hahn’s results leave trans men on hormone therapy with a lot of unanswered questions such as: “Wait, I’m losing gray matter? Don’t I need that stuff? What if I, as a professional writer, no longer a sentence together can string? Grunt! Grunt! Me no talk good. Why?”


As a trans guy, my gut tells me that I need all the gray matter I can get. Common sense and more general studies of brain plasticity and adaptability suggest that the continued daily use of advanced language skills will probably go a long way toward retaining those skills, come what may. Brains are versatile things, and research shows that individuals who undergo brain surgery or experience brain damage are often able to compensate or relearn lost skills. While the Hahn study concerned me, I didn’t allow a single researcher’s interpretation of the MRIs of a handful of subjects frighten me away from taking a positive and necessary medical step in my transition.

Still, it would be nice to have more research on the possible negative consequences of hormone therapy on transgender people, and what, if anything, can be done to mitigate them. Our understanding of the effects of cross sex hormones (the clinical term for therapy to bring the hormonal balance in line with the opposite sex) on transgender patients is woefully incomplete, which puts an individual considering hormone therapy in the unfortunate position of having to decide whether the risks and rewards of treatment are worthwhile without fully understanding what those risks and rewards are.

The contentious ongoing debate over sex differences between males and females not only overshadows transgender individuals’ concerns about their treatment, it seems at times to actively undermine attempts to learn more about how transgender patients react to treatment. For instance, Lise Eliot, the author of Pink Brain, Blue Brain, which downplays the significance of brain-based differences between the sexes, was quoted in an article for Healthline criticizing Hahn’s study by saying, in part, “any neural changes after testosterone exposure could also result from the new experience of living as a male.” Since the study looked at female-to-male transitioners roughly four weeks after they started testosterone, anyone familiar with the process could tell you that there is no significant social change that early in the process. While some factor other than testosterone may have played a role in the changes the trans men’s brains underwent compared with the female control group, that factor can’t have been that they were newly passing as male, because it takes at least five or six months for the physical changes from testosterone to accrue to the point where trans men start passing as male if they weren’t before, and there are no significant changes in outward appearance after four weeks. Eliot, a cis female neuroscientist, felt empowered to weigh in as an expert on a topic she apparently hadn’t even cursorily researched at the time she was quoted.

While the desire to emphasize similarities between men and women is understandable, even admirable, there’s an impulse to dismiss findings that suggest testosterone causes structural changes in human brains, when the actual studies that are out there, although they are preliminary, seem to point in the opposite direction. For transgender patients, information about what these hormones actually do to us is more important than a generalized impulse to shore up equality between the sexes by downplaying difference.

Evan Urquhart (formerly Vanessa Vitiello Urquhart) is working to improve comments on Slate and is a regular contributor to Outward.