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.

The European Association of Urology guideline gives the drug figures for the same kind of measurement. Finasteride reduces circulating DHT by around 70% and dutasteride by around 95%; inside the prostate, both reduce it by between 85% and 90%. The gap with that 32% is not a nuance, it is a difference of scale.

Behind that distance lies a difference of mechanism. 5-alpha-reductase has two isoforms that matter here, and finasteride was designed to block one of them selectively. The components of the extract — free fatty acids such as lauric or oleic acid, and phytosterols such as beta-sitosterol — act on both without selectivity and with far less potency.

It has also been credited with anti-inflammatory and antiproliferative effects, without any of them translating into a demonstrated clinical result.

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.

Prostate

The first of those two trials, published in 2006, followed 225 men for a year on 320 mg a day of an extract obtained with carbon dioxide. The difference on the urinary symptom scale was 0.04 points in favor of saw palmetto, with a confidence interval that crosses zero. Nor was there any difference in urinary flow, in prostate size or in quality of life.

The second, from 2011, escalated the dose: 369 men, ethanolic extract, from 320 to 640 and then to 960 mg a day over seventy-two weeks. By the end, the placebo group had improved slightly more than the active group.

A difference of less than three points on that symptom scale is considered too small for the patient to notice. Here we are talking about tenths.

The 2023 Cochrane review pooled twenty-seven studies and 4,656 participants and concluded that there is little or no difference against placebo, with high-certainty evidence, the highest grade that methodology grants.

The 2019 Chinese trial recruited 354 patients; 325 entered what the paper calls an “intention-to-treat analysis”, and followed them for twenty-four weeks. Its authors report improvement in symptoms and in urinary flow, and declare no conflicts of interest. What we have not been able to verify is the size of that improvement.

Neither of the two negative trials used the extract the European regulator recognizes, the one obtained with hexane. That detail underpins the usual defense: it is not that saw palmetto does not work, it is that the wrong extract was tested. It has a real basis, because the extracts are not chemically equivalent. And it has a counterweight: many of the studies supporting the hexanic extract are funded or signed by people linked to the laboratory that makes it. Both readings remain open.

Hair loss

Four groups, eighty people assigned, seven dropouts and seventy-three analyzed. The per-protocol analysis was done only with those who completed the study, not with everyone assigned, a criterion that tends to favor the product.

The figures that circulate from that trial, 29% less hair loss with the capsule and 22.19% with the topical application, are reductions from each group’s own baseline, not differences against placebo. The comparison against placebo does exist and is significant, but the paper presents it in a figure and does not publish its magnitude.

The values in the table show something the percentages hide. In the comb test, the capsule group went from 19.56 to 13.89 hairs and the placebo group went from 19.32 to 22.84. Part of the distance between them does not come from the product reducing hair loss, but from hair loss increasing significantly in the placebo group.

On DHT in blood, it describes a 1.29-fold reduction from baseline with the capsule, also significant against placebo. It gives no percentage for that difference and we do not calculate one ourselves.

The product tested is a proprietary extract and four of its authors were linked to the manufacturing company at the time of publication. The paper nevertheless declares that no conflicts of interest exist.

We have found no independent trial of saw palmetto on its own for hair loss. Nor any in female pattern hair loss.

Sport

Inhibiting 5-alpha-reductase lowers DHT, not testosterone. The enzyme turns one hormone into the other, so the claim that saw palmetto raises testosterone does not describe what it does.

The only trial we located that measured androgens in blood did so in men with prostatic hyperplasia, not in athletes, and with the manufacturer’s product. Free testosterone rose by 0.23 units and total testosterone fell in all three groups without reaching significance. Not even the most favorable study so far has found an anabolic effect.

So far there are no trials on strength, muscle mass, power or oxygen uptake. None. If one appears we will publish it as soon as we hear of it.

Nor have we found any on whether it prevents the hair loss associated with anabolic steroid use. Reasoning by analogy does not hold: many synthetic anabolic steroids do not need 5-alpha-reductase to act, so blocking it does not change their effect on the follicle.

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 5-alpha-reductase inhibitor drugs lower PSA by roughly half, which forces the result to be corrected when interpreting a prostate cancer screening test. A 2013 analysis found no such effect with saw palmetto: PSA behaved just as it did on placebo.

That single trial analyzed seventy-two participants and had eleven primary outcomes. Only one turned out significant, and by a narrow margin. With eleven comparisons, one coming out positive by chance is what you would expect, and that is why a trial is judged by its primary outcome and not by the best of its results. It was funded in part by the manufacturer of the product.

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 320 mg a day do not come from a dose-finding study that established an optimum. They are the dose in the summary of product characteristics of the first extract registered as a medicine, and later trials adopted it. The only published escalation tried 640 and 960 mg without finding any additional benefit.

The published trials last between twelve and seventy-two weeks, so there is no data on what happens after a year and a half of continuous use.

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.

What does not exist is a published, standardized human pharmacokinetic profile. We have not located consistent data on what proportion of each component reaches the blood, at what concentration or for how long it stays there. Nor are there comparisons of bioavailability between the different extracts.

That gap has a practical consequence. Two extracts of different chemical composition could behave the same inside the body or very differently, and without absorption data there is no way to know. That is why a negative trial with one extract does not settle the discussion about another.

A 2019 study compared the composition of several commercial extracts by metabolomic analysis and found that they are not interchangeable: they differ in their fatty acid profile and in their minor compounds. Four of its seven authors belonged, at the time of publication, to the research institute of the laboratory that makes the hexanic extract. Nor have we been able to verify which extract the 2019 Chinese trial used.

Below those three there is a second category of products: the raw oil of the fruit, the powdered fruit and tinctures. We have not located randomized trials evaluating them. Sharing a plant does not imply sharing behavior.

The usual label declares a percentage of total fatty acids. That number does not indicate which solvent the product was obtained with, so it does not allow you to know which of the extracts you have in front of you.

The extract used in the 2019 Chinese trial is not characterized in the information we have been able to verify, so it does not appear in this table.

There is no quality seal specific to saw palmetto. There are independent analyses that have compared commercial products, and the most recent quantified twenty-eight of them: total fatty acids ranged from 0.796% to 89.923%. Under the same name on the label there is room for products two orders of magnitude apart.

What is documented is substitution: a bulletin from the program that monitors adulteration of botanical products describes the replacement of the fruit oil with cheaper vegetable oils, such as palm or coconut. It is a technical bulletin, not a peer-reviewed study, and it is worth reading with that label attached.

Detecting that substitution is beyond the buyer. The percentage of fatty acids on the label can be reached with oils that do not come from the plant, because it measures how much fat there is, not where it comes from.

In Spain the authorized product is a medicine and is manufactured under pharmaceutical quality standards, with a control of composition that a food supplement is not required to meet. Outside that framework, the guarantee depends on each manufacturer.

The analysis of the twenty-eight products (Chughtai 2023) was partly funded by Valensa International, and the only one of the twenty-eight that met the criteria of the United States Pharmacopeia (USP) is a product from that same company. Chughtai also declares consultancies with several companies in the sector. The measured range remains the most complete data we have on product variability and the conflict does not void it, but it is worth reading knowing who funded it and which product came off best.

A qualification within the range itself: the nine lipid extracts on their own run from 56.970% to 89.923%. The lower end of the whole set, 0.796%, belongs to the powder category, whose ceiling is 23.745%. The “two orders of magnitude” cited above mixes different product categories; within a single category, the variability is smaller.

The experiment that would settle the discussion has not been done: a trial comparing, within the same study and on the same patients, the hexanic extract against the ethanolic one and the one obtained with carbon dioxide. Until it exists, the hypothesis that the solvent explains the divergence in results can neither be confirmed nor ruled out, because each extract has been tested in different populations and by different teams.

Nor has the independent replication been done: a large trial of the hexanic extract funded and signed by people with no link to whoever makes it.

On memory, attention or any other cognitive function we have located no trial at all. Neither for nor against. There is nothing to report, and that is the complete answer.

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.

The trials say one thing and the published cases say another, and both can be true at once. The Cochrane review found a risk of adverse effects practically identical to placebo, with a ratio of 1.01. Case reports, by contrast, collect rare episodes that a trial of a few hundred people over a few months does not get to see: a hemorrhage during an operation, a pancreatitis, a case of erectile dysfunction. A trial measures the frequent and a published case records the exceptional.

The medicine’s summary of product characteristics also lists gynecomastia among the possible effects.

Urinary symptoms have more than one possible cause and only a medical assessment tells them apart. Taking something on your own to make them more bearable does not change what is producing them.