Finasteride

A 2026 systematic review of 41 studies on 5-alpha-reductase inhibitors in androgenetic/male- or female-pattern hair loss found sexual adverse events reported in 1.9-6.7% of men on oral finasteride 1 mg versus 0.9-3.9% on placebo, and in 4.1-12.0% of men on dutasteride 0.5 mg versus 4.0-5.0% on placebo, with most events described as mild and reversible after stopping treatment; no consistent sexual adverse effects were reported in women treated for hair loss.^[2]

• Abstract-checked; individual per-study data behind the 41-study synthesis were not independently re-verified in this batch.
• Reported ranges span multiple trials of differing design and duration in an androgenetic-alopecia population; they are not a single pooled point estimate and do not quantify risk in anabolic-androgenic-steroid users.
• "Mild and reversible" reflects reporting in the synthesized trials as characterized by this review's authors, not an independent adjudication in this dossier. No qualified clinical review.

A 2026 pharmacovigilance disproportionality study using FAERS and EudraVigilance spontaneous adverse-event reports (2002-2025) identified finasteride among 19 cross-validated high-risk drugs for male infertility signals, and reported that finasteride specifically satisfied both dechallenge and rechallenge criteria in this database analysis, which the authors describe as strong evidence for causality within this study design. Dutasteride and testosterone were also named among the 19 high-risk drugs, without the same dechallenge/rechallenge detail reported in the abstract.^[3]

• Passive spontaneous-reporting pharmacovigilance databases generate disproportionality signals, not confirmed incidence rates or a validated causal mechanism beyond the dechallenge/rechallenge criterion reported for finasteride.
• Abstract-checked only; the underlying per-case data supporting the dechallenge/rechallenge finding were not independently inspected in this batch.
• A reporting-database signal is not proof of a specific individual risk and does not by itself establish an incidence rate in any particular population. No qualified clinical review.

Two placebo-controlled trials found that oral finasteride slowed hair loss and improved hair-count measures (+107 hairs at 1 year and +138 at 2 years versus placebo, from a baseline of 876 hairs in the studied scalp area) in men with androgenetic alopecia. These findings do not establish protection from the systemic risks of anabolic-androgenic steroids.^[1]

• Alopecia-specific population and formulation; not a trial of AAS users.
• Abstract-checked; full paper not confirmed open access as of 2026-09-09. No qualified clinical review.

A rat experiment combining finasteride with nandrolone decanoate reported worse cardiac hypertrophy and cytokine imbalance, but fewer bone-marrow genotoxicity markers, than nandrolone alone; the cardiac and bone-marrow results came from two separate rat cohorts with different dosing schedules (4 weeks versus 3 days), not the same animals. Together with earlier receptor-binding work that tested neither finasteride nor dutasteride, this raises a mechanistic concern; human clinical effects and their magnitude remain unknown.^[4][5]

• Preclinical experiment with intraperitoneal finasteride in n=7/group (cardiac) and n=6/group (bone marrow) rat cohorts; no human pair safety estimate.
• Opposite effects across organs, and the two organ findings come from different experimental protocols, arguing against a blanket claim that all effects worsen.

Laboratory experiments found reduced androgen-receptor affinity after nandrolone underwent 5-alpha reduction. The 1985 study tested neither finasteride nor dutasteride and did not establish human hair-loss or prostate outcomes; an interaction inferred from that study is mechanistic.^[5]

• Rat and cell experiments cannot quantify clinical benefit or harm for either named pair.