Saw palmetto is one of the most well-studied herbal supplements, and the evidence consistently shows it is well tolerated with no serious long-term side effects for most people. Two large NIH-funded clinical trials, each lasting up to 18 months, found no significant safety concerns even at doses three times the standard amount. That said, there are some mild, recurring side effects worth knowing about, along with a few rare risks that deserve attention.
What the Largest Trials Found
The best safety data comes from the CAMUS trial, a rigorous NIH-sponsored study that tracked adverse events at 12-week intervals over 18 months. Serious adverse events occurred at identical rates in the saw palmetto and placebo groups: 18 events in the supplement group versus 17 in the placebo group, a statistically meaningless difference. No deaths occurred in either group.
Among the more than 1,000 non-serious adverse events recorded across all participants, only 1.2% were judged to be probably related to the supplement. Over 83% were considered unlikely or definitely unrelated. The rate of minor adverse events was slightly higher in the saw palmetto group (3.01 per participant versus 2.63 for placebo), but this difference was not statistically significant. A separate systematic review of all available data reached the same conclusion: saw palmetto is well tolerated by most users, most adverse events are mild and easily reversible, and there is no evidence of drug interactions in clinical trials.
Common Mild Side Effects
The side effects that do show up tend to be digestive. Abdominal pain, diarrhea, and nausea are the most frequently reported complaints. Fatigue, headache, and rhinitis (a stuffy or runny nose) also appear in the literature. These symptoms are generally mild and tend to resolve on their own. In clinical trials, they occurred at rates only marginally higher than placebo, making it difficult to say with certainty that saw palmetto caused them rather than coincidence.
Hormonal Effects and Sexual Health
Saw palmetto works by blocking an enzyme called 5-alpha reductase, which converts testosterone into a more potent form called DHT. It reduces DHT’s ability to bind to receptors by roughly 50%. This is the same basic mechanism used by prescription drugs like finasteride for enlarged prostate and hair loss, which raises the question of whether saw palmetto carries similar hormonal side effects.
The short answer: it appears to cause far fewer problems. In head-to-head comparisons, saw palmetto produced fewer complaints of decreased libido and erectile difficulties than finasteride. Saw palmetto users also scored better on sexual function questionnaires. Decreased libido has been reported in some cases, and breast tissue enlargement (gynecomastia) is theoretically possible given the hormonal mechanism, but these effects are uncommon in trial data.
Dropout rates offer another useful comparison. In a meta-analysis of randomized trials, 9.1% of saw palmetto users withdrew compared to 11.2% for finasteride and 7.0% for placebo. That suggests most people tolerate it reasonably well over time.
Does It Mask Prostate Cancer Screening?
One concern that comes up often is whether saw palmetto lowers PSA levels the way finasteride does, potentially hiding early signs of prostate cancer on a blood test. The CAMUS trial specifically investigated this question and found that saw palmetto does not meaningfully affect PSA levels, even at doses well above the standard amount. Changes in PSA were virtually identical between the supplement and placebo groups over the full study period. Clinicians do not need to adjust PSA readings for men taking saw palmetto.
Liver and Pancreas Risks
Long-term use of saw palmetto has not been linked to rising liver enzymes in clinical trials. In controlled studies comparing saw palmetto to placebo in hundreds of men, liver enzyme elevations occurred at the same rate in both groups (roughly 11% to 17%, which is normal background variation). The NIH’s LiverTox database rates saw palmetto as a “possible, rare cause of clinically apparent liver injury,” the second-lowest concern level.
A handful of case reports do exist. In those rare instances, symptoms appeared within one to two weeks of starting the supplement, resembled acute viral hepatitis, and resolved within one to three months after stopping. Some of those cases involved other possible causes of liver disease, making it hard to pin the blame solely on saw palmetto.
Pancreatitis has also been reported in isolated cases. One involved a man who had used saw palmetto intermittently for four years before developing symptoms that resolved within days of stopping. Another case involved a man with a history of acid reflux who developed epigastric pain after three years of use. These remain extremely rare, and no pattern has emerged in clinical trials.
Bleeding Risk and Blood Thinners
Early case reports raised concerns that saw palmetto might increase bleeding risk, particularly around surgery. More recent and rigorous evidence has overturned that worry. Two randomized controlled trials specifically examined whether saw palmetto increases bleeding during prostate surgery and found no association. A 2022 review in Baylor University Medical Center Proceedings placed saw palmetto in the “no risk” category for surgical bleeding, alongside fish oil and ginseng.
The interaction with warfarin (a common blood thinner) is classified as “doubtful.” One case report described a modest increase in blood-thinning effect in a man who took a saw palmetto product alongside warfarin, and lab studies suggest saw palmetto may inhibit an enzyme involved in warfarin metabolism. But clinical evidence of a meaningful interaction remains thin. If you take blood-thinning medications, it is still reasonable to mention your saw palmetto use to your prescriber, since even a small shift in blood clotting can matter for people on those drugs.
What the Evidence Doesn’t Cover
The longest high-quality trials run about 18 months, which limits what we can say about use spanning many years. The trials also enrolled hundreds, not tens of thousands, of participants. That sample size is large enough to detect common problems but too small to catch very rare events. The handful of case reports involving liver injury and pancreatitis are a reminder that uncommon reactions can still occur in individual people, even when they don’t show up in controlled studies.
Saw palmetto products also vary widely in composition and quality, since dietary supplements are not regulated as strictly as prescription drugs. The safety data from clinical trials used standardized extracts with verified contents. Products purchased over the counter may differ in concentration, purity, or the presence of other ingredients, which introduces uncertainty that the trial data cannot account for.