Androgenetic alopecia (AGA) affects roughly 50% of men by age 50 and up to 40% of women by age 70, making it the most common cause of hair loss in both sexes. Yet the treatment landscape is not symmetric. The same drugs — minoxidil, finasteride, spironolactone — appear in guidelines for both men and women, but the evidence supporting their use differs substantially by sex, and the pattern of hair loss itself follows different anatomical distributions.
This analysis examines the evidence for the three most commonly used pharmacological treatments — minoxidil, finasteride, and spironolactone — across both sexes, and assesses where the evidence is robust, where it is extrapolated, and where it is genuinely absent.
Sex Differences in AGA: Ludwig vs. Hamilton-Norwood
Male AGA follows the Hamilton-Norwood scale: bitemporal recession progressing to vertex thinning and eventual confluence. The pattern is driven by dihydrotestosterone (DHT) acting on genetically sensitive follicles, causing progressive miniaturization. The frontal and vertex regions are most sensitive; the occipital region is typically spared, which is why it serves as the donor site for hair transplantation.
Female pattern hair loss (FPHL) follows the Ludwig scale: diffuse thinning over the crown with preservation of the frontal hairline. The pathophysiology is less well understood than male AGA. Androgens play a role — FPHL is more common after menopause and in women with hyperandrogenism — but many women with FPHL have normal androgen levels, suggesting additional mechanisms including local androgen receptor sensitivity, prostaglandin signaling, and inflammatory pathways. This mechanistic uncertainty complicates treatment selection.
The distinction matters clinically because treatments targeting the androgen pathway (finasteride, spironolactone) have a clearer mechanistic rationale in male AGA than in FPHL, where the androgen contribution is variable.
Minoxidil 2% vs. 5% in Women
Minoxidil is the only FDA-approved topical treatment for both male and female AGA. The approved concentrations differ: 5% for men, 2% for women (though 5% is now also approved for women as a foam formulation). The evidence base for women is smaller than for men but is the most robust of any treatment in FPHL.
The pivotal trials for 2% minoxidil in women (Olsen et al., 2002; DeVillez et al., 1994) demonstrated statistically significant increases in non-vellus hair count versus placebo at 32 weeks, with approximately 20–30% of women showing moderate or better regrowth. The 5% foam formulation was approved based on a non-inferiority trial showing comparable efficacy to 2% solution with a better tolerability profile (less facial hypertrichosis due to the foam vehicle).
A 2019 Cochrane review of minoxidil for AGA found that 5% minoxidil was more effective than 2% in men, but the evidence for a dose-response advantage in women was less clear. The 5% solution in women showed higher rates of facial hypertrichosis (unwanted facial hair growth) than 2%, which affects tolerability and adherence. The 5% foam formulation appears to reduce this side effect due to faster drying and less drip onto the face.
Finasteride in Women: Off-Label, Teratogenicity Risk
Finasteride (1 mg/day for AGA, 5 mg/day for BPH) is FDA-approved only for men. Its use in women is off-label and carries a significant contraindication: finasteride is a Category X teratogen in pregnancy. It inhibits 5-alpha reductase, preventing conversion of testosterone to DHT, and can cause feminization of male fetuses. Women of childbearing potential must use reliable contraception if prescribed finasteride.
The evidence for finasteride in postmenopausal women with FPHL is mixed. A 2012 RCT by Iorizzo et al. (n=37) found no significant difference between finasteride 1 mg/day and placebo in postmenopausal women with FPHL over 12 months. A larger trial by Trüeb et al. found modest benefit at higher doses (2.5 mg/day) in women with elevated androgen levels, but not in women with normal androgens.
The current evidence suggests finasteride may be effective in women with documented hyperandrogenism but has limited evidence in normo-androgenic FPHL — the majority of cases. This is a meaningful limitation given that finasteride is sometimes prescribed broadly for FPHL without androgen testing.
The Claim
"Finasteride works for hair loss in both men and women — it blocks DHT, which is the cause of androgenetic alopecia in everyone."
(Representative claim from consumer hair loss forums and some direct-to-consumer telehealth platforms.)
What the Evidence Actually Shows
The claim overstates the evidence. Finasteride has robust RCT support in men with AGA. In women, the evidence is substantially weaker — the largest RCTs in postmenopausal women with FPHL showed no significant benefit at 1 mg/day. Benefit appears limited to women with documented hyperandrogenism, who represent a minority of FPHL cases. The teratogenicity risk is a serious contraindication in premenopausal women. The mechanistic claim that DHT is "the cause" of AGA in women is an oversimplification of a more complex and incompletely understood pathophysiology.
Spironolactone Evidence
Spironolactone is an aldosterone antagonist with anti-androgenic properties — it blocks androgen receptors and reduces adrenal androgen production. It is used off-label for FPHL, typically at doses of 100–200 mg/day. It is not used in men for AGA due to feminizing side effects (gynecomastia, sexual dysfunction).
The evidence base for spironolactone in FPHL is limited. A 2020 retrospective study by Sinclair et al. (n=100) found that 44% of women with FPHL showed improvement on spironolactone over 12 months, but this was an uncontrolled observational study. The only published RCT of spironolactone for FPHL (Famenini et al., 2015, n=40) found significant improvement in hair density versus placebo at 6 months. However, the trial was small and short-duration.
A 2023 systematic review by Lacarrubba et al. identified only 3 RCTs of spironolactone for FPHL, all with small sample sizes and methodological limitations. The review concluded that spironolactone showed promise but that the evidence was insufficient to make definitive recommendations. Spironolactone requires monitoring for hyperkalemia and is contraindicated in pregnancy.
Platelet-Rich Plasma (PRP)
PRP involves injecting concentrated autologous platelets into the scalp to stimulate growth factors. It is used in both men and women with AGA. The evidence is more consistent in men than women, though both bodies of literature are limited by small sample sizes and heterogeneous protocols (centrifugation speed, platelet concentration, injection technique, number of sessions).
A 2019 meta-analysis by Gupta and Carviel found significant improvements in hair density and thickness with PRP versus placebo in AGA, but noted high heterogeneity across studies. Sex-stratified analyses were not consistently reported. PRP is not FDA-approved for AGA and is not covered by insurance; costs typically range from $1,500–$3,500 per treatment course.
Verdict: Mixed Evidence
The evidence for AGA treatment differs substantially by sex. Minoxidil has the strongest evidence in both sexes and is FDA-approved for both, though the dose-response relationship in women is less clear than in men. Finasteride has robust evidence in men but weak evidence in women with normal androgen levels, and carries a serious teratogenicity risk. Spironolactone has limited RCT evidence in women and no role in men for AGA. PRP evidence is promising but methodologically weak in both sexes. The common marketing framing that these treatments work equivalently across sexes is not supported by the evidence. Evidence rating: 3/5.