Finasteride and dutasteride belong to a drug class called 5-alpha-reductase inhibitors, which block the enzyme that converts testosterone into dihydrotestosterone, the androgen behind follicle miniaturization in pattern hair loss. They lower circulating DHT by roughly 70 percent while generally leaving testosterone levels where they are. A team at Wrocław Medical University and Wrocław University of Science and Technology went looking for every study that measured sexual side effects in people taking these drugs for hair loss specifically, rather than for an enlarged prostate, which is where most of the older safety data comes from. They searched four databases through December 2025 and ended up with 41 studies, 33 of which looked directly at pattern hair loss populations. Across 11 studies covering 7,116 men on oral finasteride, sexual adverse events were reported in 0.25 to 7.9 percent of treated patients, against 0.9 to 3.4 percent in the placebo and control groups. In the original 1998 trial of 1,553 men, decreased libido at twelve months was reported by 1.9 percent on finasteride and 0.9 percent on placebo, erectile dysfunction by 1.4 percent and 1.3 percent, and ejaculation disorder by 1.0 percent and 0.4 percent. Oral dutasteride, which blocks both forms of the enzyme instead of one, ran higher at 0 to 11.7 percent across three studies. Topical finasteride ran lowest, with no sexual adverse events reported across four studies and 167 patients, and in a phase III trial of 458 men comparing the two head to head the rate was 2.8 percent on topical, 4.8 percent on oral and 3.3 percent on placebo. Across six studies covering 376 women treated for female pattern hair loss, no sexual adverse events were reported.

The authors are careful about what those numbers can carry, and their caveats matter as much as the figures. Differences in study design, dose and the definition of sexual dysfunction meant nothing could be pooled into a single estimate, so this is a narrative synthesis and not a meta-analysis. They also report that 8,320 of the 9,133 records they sought could not be retrieved as full text, roughly 91 percent, mostly gray literature pulled in by a broad Google Scholar search, and they note the review was not registered in advance with PROSPERO. Two of their findings cut in opposite directions. In several of the placebo-controlled trials, the rate of sexual complaints in the placebo group was similar to the rate in the treated group, which the authors discuss as a nocebo effect, where being warned about a side effect makes it more likely to be reported. A separate meta-analysis they cite found that in hair loss trials specifically the pooled estimates were not statistically significant, with a relative risk of 1.21 for sexual dysfunction and a confidence interval of 0.85 to 1.72 that includes no effect at all. Going the other way, seven studies covering more than 12,221 people examined persistent symptoms after stopping the drug, often called post-finasteride syndrome, with reported rates running from 1.4 percent for persistent erectile dysfunction up to 94 percent for libido complaints. The authors flag that range as coming from self-selected, uncontrolled survey populations, and they state plainly that the prevalence, the causal relationship and the mechanism all remain uncertain. One controlled study they cite found no evidence of androgen deficiency or ongoing enzyme suppression in men reporting persistent symptoms, though it did find differences in mood and brain activity that tracked with those symptoms. The topical finasteride result, which looks the cleanest of the lot, rests on 167 patients across four studies with follow-up measured in months, so it is the thinnest dataset here rather than the strongest. Data in women are described as limited throughout, and the authors note that oral 5-alpha-reductase inhibitors carry a teratogenic risk, making strict pregnancy prevention essential. Their overall framing is that most sexual side effects recorded in controlled hair loss studies are infrequent, mild and reversible, that individual susceptibility varies, and that better long-term studies using standard definitions are needed to work out who is actually at risk.

Here's the study: Złotowska A, Jastrząb-Miśkiewicz B, Krajewski PK. Sexual dysfunction associated with 5α-reductase inhibitors in the treatment of androgenetic alopecia: a systematic review. Frontiers in Medicine, 2026;13:1787706. doi:10.3389/fmed.2026.1787706. Indexed on PubMed (PMID 42396141). Read the full text here.

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