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Fin5.5
Finasteride Research
Mostly mechanism / observationalLimited safety
8 peer-reviewed studies
What the evidence says
Mostly mechanism / observational
Most Finasteride studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from medium-quality meta-analyses and randomised trials published 1998–2024 with a typical study size of 3,040 participants.
Based on 8 studies · 1 meta-analysis · 5 RCTs · 28,075 total participants
Confidence
High
By outcome
Hair loss (androgenetic alopecia)
Mostly mechanism / observational4 studies
Prostate & male hormones
Mostly mechanism / observational4 studies
Mood & psychological effects
Too few graded studies2 studies
Safety profile
Too few graded studies2 studies
Steady research
2 studies in the last 5 years · Latest meta-analysis: 2024
199820112024
1RCTn=1,553 · large study1998
In two 1-year trials of 1553 men, finasteride 1 mg/day increased scalp hair count and was judged to improve male pattern hair loss versus placebo.
Kaufman, Olsen, Whiting, Savin, DeVillez, Bergfeld · Journal of the American Academy of Dermatology (1998)
Pivotal double-blind randomized, placebo-controlled trials of finasteride 1 mg/day for male pattern hair loss
Increased scalp hair counts and improved investigator/patient and photographic assessments
Finasteride inhibits type-II 5α-reductase, lowering serum and scalp DHT
Finasteride reduced the prevalence of prostate cancer by 24.8% over seven years, but high-grade (Gleason 7-10) tumors were more common in the finasteride group.
Thompson, Goodman, Tangen, Lucia, Miller, Ford · The New England journal of medicine (2003)
PCPT: RCT of finasteride 5 mg/day vs placebo for prostate-cancer prevention in 18,882 men
Reduced overall prostate-cancer prevalence by ~25% over seven years
Important nuance: more high-grade (Gleason 7-10) tumors in the finasteride arm
Sexual effects including erectile dysfunction and decreased libido were reported in as many as 3.4 to 15.8 percent of men, and depression is listed as a side effect.
Hirshburg, Kelsey, Therrien, Gavino, Reichenberg · The Journal of clinical and aesthetic dermatology (2016)
Systematic review of 5α-reductase-inhibitor adverse effects across prostate, sexual, and psychological domains
Sexual effects (ED, decreased libido, reduced ejaculate) reported in ~3.4-15.8% of men
Notes the NIH post-finasteride syndrome entry and depression listed on packaging
8Observational2021
Disproportionality analysis of the WHO VigiBase found a signal for suicidality and psychological adverse events with finasteride, particularly in younger patients and those using it for alopecia.