Saw Palmetto: What the Trials Actually Show for Prostate Symptoms, Hair Loss and Safety

What saw palmetto is

Saw palmetto (Serenoa repens) is a small palm native to the south-eastern United States. Its berries have been used for urinary complaints since the nineteenth century, and extracts of the berry — rich in fatty acids and plant sterols including beta-sitosterol — became one of the most widely used treatments for enlarged prostate symptoms in Europe, where they are sold as medicines, and one of the top-selling supplements in the United States.

How it is supposed to work

Laboratory studies suggest saw palmetto extracts weakly inhibit 5-alpha reductase (the enzyme that makes DHT, which drives prostate growth), reduce inflammation, and have effects on smooth muscle similar to alpha-blockers. None of these effects has been demonstrated to a clinically meaningful degree in men.

What the trials show

The history runs in two phases.

Before 2006, dozens of small, short trials — many lacking proper blinding or placebo — reported that saw palmetto improved urinary symptoms and flow, and early meta-analyses concluded it worked about as well as finasteride.

From 2006, two large, rigorous trials tested that conclusion:

• STEP (2006, New England Journal of Medicine): 225 men with moderate to severe symptoms took 160 mg twice daily of a standardized extract or placebo for a year. No difference in symptom score, flow rate, residual volume, prostate size or quality of life.
• CAMUS (2011, JAMA), funded by the NIH: 369 men took saw palmetto escalating from 320 mg to 960 mg per day — three times the usual dose — or placebo for 72 weeks. Symptom scores improved by 2.2 points on saw palmetto and 3.0 on placebo. No secondary outcome differed, including PSA, flow, residual volume, sexual function and sleep.

The 2023 Cochrane review pooled 27 randomized trials (4,656 men) and found an average improvement in symptom score of about 0.9 points versus placebo, rated high certainty — well below the 3-point change considered noticeable to a patient — and no effect on flow rate or prostate size.

The extract argument

Defenders of saw palmetto point out that "saw palmetto" is not one product. Extracts differ in solvent (hexane, ethanol, supercritical CO₂) and in fatty acid content, and the hexane-extracted lipidosterolic extract sold as Permixon in Europe has its own body of trials showing modest symptom improvement comparable to tamsulosin in some. European urology guidelines give this specific extract a weak recommendation. The counter-argument is that CAMUS used a well-characterized extract at high dose and found nothing, and that the Permixon trials were mostly industry-sponsored.

For a buyer, the practical point is that the extract in most over-the-counter products has not been shown to work, and that products vary too much to assume one is like another.

Evidence by use

Doses studied

320 mg per day of a lipidosterolic extract (standardized to 85–95% fatty acids and sterols), usually as 160 mg twice daily. CAMUS tested up to 960 mg with no added effect. Whole-berry powders and teas contain far less active material and were not what trials tested.

Safety

Saw palmetto is well tolerated. Side effects are mild and infrequent: stomach upset, headache, and occasionally reduced libido. The CAMUS safety analysis found no meaningful difference from placebo at up to 960 mg. It does not affect PSA, so it does not mask cancer detection the way finasteride can. Isolated reports of liver or pancreas problems and of bleeding during surgery exist; it is sensible to stop it two weeks before an operation. It should not be used by women who are pregnant, and has no role in children.

Where it appears in supplements

Saw palmetto is the anchor ingredient of almost every prostate supplement, often combined with beta-sitosterol, pygeum, nettle root, zinc, lycopene and pumpkin seed. Labels rarely state the extract type or fatty acid content, and "saw palmetto berry powder 500 mg" is not equivalent to 320 mg of standardized extract. See prostate supplement research.

Bottom line

For most men buying it, saw palmetto is a safe way to spend money on a modest placebo effect. Men with bothersome urinary symptoms have treatments that work — alpha-blockers within days, 5-alpha reductase inhibitors over months — and a doctor who can rule out the other causes of a weak stream. The question Does saw palmetto work for an enlarged prostate? gives the shorter version.

Frequently asked questions

References