Too much testosterone might kill you during COVID-19 - and too little testosterone might kill you just as fast.
That's not a riddle. That's the actual, maddening biological reality that a team of researchers just laid bare in a new study published in Signal Transduction and Targeted Therapy, and it plays like a jazz chord nobody expected to hear in the middle of the set (Yuan et al., 2026).
The Goldilocks Zone That Doesn't Exist
Here's the tune: men die from COVID-19 at roughly two to three times the rate women do. That stat has been consistent across countries, age groups, and variants since the pandemic's opening notes. The prime suspect? Testosterone. But the relationship between the male hormone and SARS-CoV-2 has never been a simple melody - it's more like a twelve-bar blues played in a time signature nobody agreed on.
Testosterone cranks up the expression of ACE2 and TMPRSS2, the two molecular doorknobs that SARS-CoV-2 grabs to break into your cells (Hoffmann et al., 2020). More testosterone, more doorknobs, more virus getting in. Simple, right? Except ICU data kept showing that men with low testosterone were the ones dying at the highest rates. Men with levels below 100 ng/dL had over eighteen times higher in-hospital mortality than those above 230 ng/dL.
So which is it - too much or too little?
Yuan and colleagues decided to stop guessing and just test both ends of the dial. Using a hamster model of COVID-19, they administered testosterone at low and high doses to both male and female hamsters, then watched what happened after SARS-CoV-2 infection. The results hit like a dissonant chord resolving into something nobody saw coming.
Both Notes Are Wrong
Both low and high doses of testosterone made male hamsters sicker. Worse survival rates. More body weight loss. Higher viral loads. Nastier lung damage. The hormone wasn't a simple villain or hero - it was running a protection racket where everyone loses.
For female hamsters, the melody was slightly different but equally strange. A low dose of testosterone actually helped them fight off infection. But crank the dose up, and it turned harmful. The same molecule, playing two completely different solos depending on who's listening and how loud you turn it up.
This dose-dependent, sex-specific behavior explains why the field has been chasing its own tail for years. Previous studies kept finding contradictory results because testosterone's role in COVID-19 isn't linear - it's a U-shaped curve of chaos (Salonia et al., 2021).
Enter Finasteride: The Key Change
Here's where the improvisation gets really interesting. If testosterone at any dose is bad news for infected males, what happens when you block it? The team reached for finasteride - yes, the same drug millions of men take for hair loss and enlarged prostates - and used it to dial down testosterone's effects.
The results were a standing ovation. Finasteride-treated male hamsters survived lethal SARS-CoV-2 challenges that killed untreated males. It prevented severe pneumonia across multiple viral strains. A hair-loss drug, potentially saving lives from a respiratory pandemic. Drug repositioning doesn't get much jazzier than that.
This isn't entirely out of left field. A small randomized clinical trial of 80 hospitalized men found that finasteride was associated with improved oxygen saturation and a 75% lower mortality rate (Goren et al., 2021). But preclinical proof of why it works has been scarce until now.
Reading the Sheet Music in the Lungs
The researchers then pulled out the transcriptomics - essentially reading every gene that was being turned on or off in infected lung tissue. The pulmonary transcriptome data revealed how testosterone amplifies the inflammatory damage that makes COVID pneumonia so deadly, and how finasteride rewrites that script. Testosterone wasn't just letting more virus in through ACE2 and TMPRSS2; it was also messing with the immune response itself, turning what should be a tight combo into a chaotic free-for-all (Qiao et al., 2021).
Women's immune systems, meanwhile, tend to mount stronger T-cell responses and more robust antibody production during SARS-CoV-2 infection - advantages partly written into the X chromosome, which carries multiple immune-related genes in duplicate (Takahashi et al., 2020).
The Encore
What makes this study sing is the practical riff at the end: finasteride is cheap, widely available, FDA-approved, and already has decades of safety data. If these hamster results translate to larger human trials, we're looking at a host-targeting therapy that sidesteps the problem of viral mutations entirely. The virus can change its setlist all it wants - finasteride is playing the venue, not the band.
For a pandemic that exposed just how differently biology treats men and women, the idea that a drug from the hair-loss aisle could rewrite the score is the kind of improvisation science does best.
References
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Yuan, L., Xiao, H., Liu, X., et al. (2026). Sexual dimorphism of COVID-19 inspires drug repositioning and host-targeting immunotherapy for viral pneumonia. Signal Transduction and Targeted Therapy. DOI: 10.1038/s41392-026-02636-1
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Hoffmann, M., Kleine-Weber, H., Schroeder, S., et al. (2020). SARS-CoV-2 cell entry depends on ACE2 and TMPRSS2 and is blocked by a clinically proven protease inhibitor. Cell, 181(2), 271-280. DOI: 10.1016/j.cell.2020.02.052. PMID: 32142651
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Salonia, A., Pontillo, M., Capogrosso, P., et al. (2021). The role of sexual dimorphism in susceptibility to SARS-CoV-2 infection, disease severity, and mortality. Molecular Aspects of Medicine, 81, 100924. DOI: 10.1016/j.mam.2021.100924. PMID: 34129909
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Qiao, Y., Wang, X.M., Mannan, R., et al. (2021). Targeting transcriptional regulation of SARS-CoV-2 entry factors ACE2 and TMPRSS2. Proceedings of the National Academy of Sciences, 118(1), e2021450118. DOI: 10.1073/pnas.2021450118. PMID: 33310900
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Takahashi, T., Ellingson, M.K., Wong, P., et al. (2020). Sex differences in immune responses that underlie COVID-19 disease outcomes. Nature, 588, 315-320. DOI: 10.1038/s41586-020-2700-3. PMID: 32846427
Disclaimer: The image accompanying this article is for illustrative purposes only and does not depict actual experimental results, data, or biological mechanisms.