Saw palmetto
Serenoa repens

In Spain, the extract of Serenoa repens is registered as a prescription-only medicine, not as a food supplement. In the European Union there is a monograph from the European Medicines Agency’s committee on herbal medicinal products, but each country sets its own dispensing status. In the United States it is sold as a supplement in any shop. This page describes what the published studies have measured and makes no recommendations.

It is the fatty extract of the fruit of Serenoa repens, a dwarf palm that grows in the south-eastern United States and only fruits there. In Spanish it is called palma enana americana.

Products sold under the same name do not contain the same thing. The solvent used to extract the fat from the fruit (hexane, ethanol or pressurized carbon dioxide) leaves different amounts of fatty acids and sterols inside. The clinical trials have been done with extracts that differ from one another.

Its proposed mechanism is inhibition of 5-alpha-reductase, the enzyme that converts testosterone into dihydrotestosterone (DHT). DHT is involved in prostate growth and in the miniaturization of the hair follicle. Saw palmetto also inhibits it, though more weakly than the drugs developed for that purpose.

Prostate. It is the most studied plant for the urinary symptoms of benign prostatic hyperplasia. The two large publicly funded trials, one of a year and another of seventy-two weeks, found no difference against placebo in symptoms, not even when the dose was tripled. A 2023 Cochrane review concludes the same with high-certainty evidence. A third large trial, carried out in China, did find improvement.

The European regulator recognizes well-established use for a single extract, the one obtained with hexane. The European Association of Urology guideline offers it with a weak recommendation, and warns with a strong recommendation that the size of the effect may be modest.

Hair loss. There is a single randomized trial with double blinding, a placebo group and saw palmetto as the only ingredient: sixteen weeks, eighty participants, a proprietary product and authors linked to the manufacturer. It reduced hair loss against placebo, both orally and applied topically, and lowered DHT in blood. The paper does not publish the size of that difference, and a good part of it comes from hair loss increasing in the placebo group.

The oral dose was 100 mg a day, less than a third of the 320 mg used for the prostate, and the proportion of hairs in the growth phase, which is the measure of whether the follicle recovers, did not improve significantly.

There is a second study, a two-year head-to-head against finasteride in one hundred men, in which 38% of those taking saw palmetto improved against 68% of those taking the drug. It is of lower quality: it had no placebo group and no one was blinded, everyone knew what they were taking. And it does not contradict the above because it did not measure the same thing: it scored before-and-after photographs of each participant and calculated what percentage of men improved, not what proportion of the hair was in the growth phase.

Finasteride is a prescription-only medicine. An open-label study of one hundred people does not establish that the two are interchangeable alternatives.

There are no trials on athletic performance, muscle mass or memory.

For adult men with moderate urinary symptoms associated with benign prostatic hyperplasia, which in Spain is the medicine’s authorized indication and is assessed by a doctor.

For hair, the studies this page is based on indicate reduced hair loss but no significant increase in hairs in the growth phase.

In women there are no trials on polycystic ovary syndrome or hirsutism, which are the two uses most often attributed to it. The only one located measured urinary symptoms in women over fifty.

The dose used in the trials matches the posology that the AEMPS, the Spanish medicines agency, authorises for the medicine: 320 mg a day of the lipidosterolic extract, in one dose or in two, with meals. The summary of product characteristics notes that four to eight weeks may pass before a response can be assessed.

The extract is a fatty fraction and its proposed active components are fatty acids and sterols, molecules that are absorbed better alongside other fats. Hence the authorized posology places it with meals.

Pregnancy, breastfeeding and women who may become pregnant. Its antiandrogenic activity raises a theoretical risk for a male fetus, by analogy with the 5-alpha-reductase inhibitor drugs. In these cases the advisable course is to consult a specialist before taking it.

Scheduled surgery. A consensus from the Society for Perioperative Assessment and Quality Improvement recommends stopping it two weeks before elective surgery. It is worth telling the surgical team.

Anticoagulation or clotting disorders. There are published cases of bleeding, isolated and few in number.

A 2009 systematic review of products containing only saw palmetto describes it as well tolerated and free of serious adverse effects, and documented no interactions with medicines in the studies it reviewed. The most frequent ones are mild and appear as often as with placebo: digestive discomfort, nausea, headache, reduced libido.

Talk to your doctor before taking it, especially if you are already on treatment for the prostate.