Benefits
Prostate symptom scores: matched placebo in the largest trials
In men with an enlarged prostate, the year-long STEP trial (225 men) and the 72-week CAMUS trial (369 men, up to 960 mg/day) found no difference from placebo in symptom scores or urine flow. A review of 27 studies rated the evidence high certainty that saw palmetto alone gives little or no benefit. A 354-man trial in China and studies of one branded extract were positive.
Urinary flow in men: no gain over placebo in independent trials
Peak urine flow and nighttime urination were measured in the large independent trials and showed no significant improvement over placebo; an earlier review found no gain in flow across three high-quality trials. A manufacturer-linked analysis of one branded hexanic extract reported fewer nighttime trips and better flow. All of these trials enrolled men.
Hair growth
Evidence is preliminary. In a small pilot of saw palmetto combined with beta-sitosterol in men with pattern hair loss, 6 of 10 men on the blend were rated improved. A company-funded trial of a proprietary extract in 60 adults, half of them women, reported higher hair counts than placebo after 90 days, but only interim results are published.
Mechanism of action
5-alpha-reductase (proposed)
Saw palmetto extract is described as an inhibitor of 5-alpha-reductase, the enzyme that turns testosterone into DHT, and this is the reason it was tested for prostate symptoms and hair loss. In people, it did not change prostate-specific antigen levels in the STEP trial or in the branded-extract analysis, and the large trials found no clinical benefit.
Clinical trials
Double-blind randomized trial of saw palmetto extract 160 mg twice daily versus placebo for one year (Bent et al. 2006, N Engl J Med).
225 men over 49 with moderate to severe symptoms of an enlarged prostate.
There was no significant difference in symptom score (mean difference 0.04 points), peak urine flow, prostate size, residual urine, quality of life or prostate-specific antigen. Side effects were similar in both groups.
Double-blind, multicenter randomized trial at 11 North American sites; saw palmetto 320 mg/day, raised to 640 and then 960 mg/day, versus placebo for 72 weeks (Barry et al. 2011, JAMA).
369 men aged 45 or older with lower urinary tract symptoms.
Symptom scores fell 2.20 points on saw palmetto and 2.99 points on placebo, a difference of 0.79 points favoring placebo. Saw palmetto was no better than placebo on any secondary outcome, and no clearly attributable side effects were found.
Cochrane systematic review of 27 placebo-controlled studies with 4,656 men (Franco et al. 2023, Cochrane Database Syst Rev).
Men, mostly over 50, with moderate urinary symptoms linked to an enlarged prostate.
In low risk of bias studies, saw palmetto alone made little or no difference to symptoms (mean difference -0.90 points at 3 to 6 months and 0.07 points at 12 to 17 months) or to quality of life, rated high certainty. Side effects were probably no different from placebo. Ten of the studies were industry funded.
Twelve-month double-blind randomized trial of the hexanic extract Permixon 320 mg/day versus tamsulosin 0.4 mg/day, with no placebo arm (Debruyne et al. 2002, Eur Urol).
704 men with urinary symptoms of an enlarged prostate in 11 European countries; 542 in the per-protocol analysis.
Symptom scores fell by 4.4 points in both groups and peak flow rose by 1.8 and 1.9 mL/s. With no placebo arm, the trial cannot separate the effect of either product from placebo response.
Six-month randomized, double-blind, placebo-controlled trial of a 160 mg/day proprietary saw palmetto fatty acid extract, sponsored by its maker, Valensa International; interim 90-day results (Ablon 2025, J Cosmet Dermatol).
60 healthy adults with self-perceived thinning hair (40 active, 20 placebo), half of them women.
Terminal and total hair counts rose more than with placebo in front and back scalp areas, and shedding fell from baseline. No adverse events were reported. These are interim results from one company-sponsored trial.