Saw palmetto is a dwarf palm of the American southeast whose berry extract has been used for prostate and urinary complaints for over a century. It is one of the most widely used herbals by older men, and in parts of Europe a standardized hexanic extract is a prescription medicine for lower urinary tract symptoms from benign prostatic hyperplasia.

The research history is unusually clean. A 1998 systematic review in JAMA pooled 18 trials and found it beat placebo and matched finasteride. Then two large, well-run, NIH-funded trials in 2006 and 2011 found nothing, including at three times the usual dose over 72 weeks, and the Cochrane review concluded it was no better than placebo. A 2018 meta-analysis restricted to the European pharmaceutical extract still finds a benefit. Both things are true, and which product you buy decides which literature applies.

The extract's fatty acids and sterols are proposed to inhibit 5-alpha-reductase, the enzyme finasteride blocks, and to act on androgen and estrogen receptors and inflammatory pathways in prostate tissue. A 1992 study reported an anti-estrogenic effect in prostate tissue of treated men. Unlike finasteride, it does not meaningfully lower PSA or shrink the prostate much in trials, which is one reason the 5-alpha-reductase story is doubted as the main mechanism at the doses used. Extracts differ a great deal in fatty acid and sterol content depending on the solvent and process, which is the standing explanation for why trials of different products disagree.

The early pooled result. The 1998 JAMA review of 18 randomized trials in 2,939 men, mean duration nine weeks, found fewer night-time voids (0.76 per night), better self-rated symptoms, higher peak urine flow (1.93 mL per second) and symptom improvement similar to finasteride, with less erectile dysfunction (1.1% against 4.9%).

The trials that changed the answer. The 2006 NEJM trial randomized 225 men over 49 with moderate to severe symptoms to 160 mg twice daily or placebo for one year: no difference in symptom score (0.04 points), peak flow, prostate size, residual volume, quality of life or PSA. The 2011 CAMUS trial randomized 369 men at 11 sites and escalated the dose from 320 to 960 mg a day over 72 weeks: symptom scores fell 2.20 points on saw palmetto and 2.99 on placebo, a 0.79-point difference favoring placebo, with no secondary outcome favoring the extract.

Cochrane. The 2012 review pooled two high-quality long-term trials (582 men) and found no superiority over placebo on the AUA symptom index (0.25 points), with the 72-week trial showing nearly identical responder rates at double and triple doses.

The European extract. A 2018 meta-analysis of 27 studies (15 randomized, 5,800 patients) of the hexanic extract Permixon at 320 mg a day found 0.64 fewer voids per night and a 2.75 mL per second gain in peak flow against placebo, symptom improvement similar to alpha-blockers and 5-alpha-reductase inhibitors, and no effect on sexual function or PSA. Observational studies were pooled with trials, and the product's manufacturer was involved.

Hair. A two-year open-label comparison in 100 men with androgenetic alopecia found 38% improved on 320 mg of saw palmetto against 68% on finasteride. A 2026 six-month placebo-controlled trial of a proprietary fatty-acid extract in 60 adults with self-perceived thinning reported higher terminal hair counts, from the product's maker.

This is the safest entry on the shelf. The CAMUS safety analysis of 357 men over 18 months at up to three times the usual dose found no difference from placebo in serious or non-serious adverse events, vital signs, prostate examination or laboratory tests. A 2009 systematic review of 40 studies found adverse events mild and similar to placebo (abdominal pain, diarrhea, nausea, fatigue, headache, decreased libido, rhinitis) and no drug interactions, with isolated serious reports of questionable causality.

Two cautions that are not about the extract. It can mask the problem: an enlarged prostate and prostate cancer share symptoms, and taking a supplement instead of seeing a doctor delays the examination that distinguishes them. And it does not lower PSA the way finasteride does, so it does not interfere with PSA screening, which is an advantage worth knowing.

A dietary supplement in the United States, sold without review of its claims. In several European countries the standardized hexanic extract is a prescription or pharmacy medicine for lower urinary tract symptoms, which is why the European trials and the American supplement trials are testing different things. No regulator has approved it for hair loss.