For decades, saw palmetto was the default herbal answer for men bothered by a weak stream or frequent bathroom trips. Early research looked encouraging, and the supplement became one of the best known prostate products in the United States. Then came two large, carefully designed, publicly funded trials, followed by an updated Cochrane review. Their results were consistent and, for fans of the herb, disappointing. This roundup walks through what those studies actually tested, what they found, and what the findings do and do not mean for you.
Why did saw palmetto look promising in the first place?
Saw palmetto (Serenoa repens) is a small palm native to the southeastern United States, and the extract comes from its berries. It is used for lower urinary tract symptoms (LUTS) linked to benign prostatic hyperplasia (BPH), the noncancerous prostate enlargement that becomes common with age. Typical complaints include a weaker urine stream, urgency, and waking up at night to urinate.
A 1998 systematic review in JAMA pooled 18 randomized trials with 2,939 men and reported modest improvements in symptom scores, nighttime urination, and peak urine flow compared with placebo (Wilt et al., 1998). But the authors also flagged real limits: the trials were short, with a mean duration of only 9 weeks, and many did not report results in a way that allowed them to be combined. Short, small studies with inconsistent reporting are exactly the kind of evidence that tends to shrink when larger, longer trials arrive.
What did the STEP trial find?
The first big test was the STEP trial (Saw Palmetto Treatment for Enlarged Prostates), published in the New England Journal of Medicine in 2006 (Bent et al., 2006). Researchers at the University of California, San Francisco randomly assigned 225 men over age 49 with moderate to severe BPH symptoms to one year of saw palmetto extract (160 mg twice a day) or a matching placebo. Neither the men nor the researchers knew who got which.
The main outcomes were the American Urological Association Symptom Index (AUASI), a standard questionnaire scored from 0 to 35, and maximal urinary flow rate. After a year, the difference between groups on the symptom score was 0.04 points, essentially zero. Flow rate, prostate size, leftover urine after voiding, quality of life, and PSA levels were also no different. Side effects were similar in both groups.
Critics raised fair questions. Was the dose too low? Was this particular extract the right one? Those questions set up the next trial.
Did a higher dose help in the CAMUS trial?
The CAMUS trial (Complementary and Alternative Medicine for Urological Symptoms) was designed to answer the dose question directly. Published in JAMA in 2011, it enrolled 369 men aged 45 or older with moderate symptoms at 11 North American sites (Barry et al., 2011). Men took either placebo or saw palmetto extract starting at the standard 320 mg per day, with the dose doubled at 24 weeks and tripled at 48 weeks, for 72 weeks in total.
Both groups improved, which is the important twist. Symptom scores fell by about 2.2 points with saw palmetto and by about 3.0 points with placebo. The difference, 0.79 points, actually favored placebo, though it was not meaningful either way. Saw palmetto was no better than placebo on any secondary outcome, including urinary bother, nighttime urination, flow, PSA, sexual function, and sleep quality. No clearly attributable side effects were found even at triple the usual dose.
That placebo improvement matters. Urinary symptoms naturally fluctuate, and people tend to enroll in studies when symptoms are at their worst. Many men will feel somewhat better over months no matter what they take, which is exactly why uncontrolled experiences and short, small trials can be misleading.
What does the Cochrane review conclude?
Cochrane reviews pool all eligible randomized trials and grade how confident we can be in the results. The 2012 update included 32 trials and 5,666 men (Tacklind et al., 2012). Combining the two high quality long-term trials, saw palmetto was not superior to placebo for symptoms. It did not improve peak urine flow in the three high quality trials, and in CAMUS it did not significantly reduce nighttime urination.
The 2023 update narrowed its focus to placebo comparisons and graded the evidence (Franco et al., 2023). Looking at 27 studies with 4,656 participants and relying on trials at low risk of bias, the reviewers found, with high certainty, that saw palmetto alone results in little to no difference in urinary symptoms or quality of life, both in the short term (3 to 6 months) and the long term (12 to 17 months). Their bottom line: saw palmetto alone provides little to no benefit for men with these symptoms. Products that combine saw palmetto with other plant extracts were judged more uncertain, with low certainty evidence.
| Study | Who and how long | Main result |
|---|---|---|
| STEP (NEJM, 2006) | 225 men, 1 year, 320 mg/day | No difference from placebo in symptoms, flow, or prostate size |
| CAMUS (JAMA, 2011) | 369 men, 72 weeks, up to 960 mg/day | No difference from placebo at any dose; placebo group improved slightly more |
| Cochrane (2012) | 32 trials, 5,666 men | Not superior to placebo for symptoms, flow, or prostate size |
| Cochrane (2023) | 27 trials, 4,656 men | Little to no difference in symptoms or quality of life (high certainty) |
Is saw palmetto safe, and does it affect PSA?
The good news in these trials is about safety. According to the National Center for Complementary and Integrative Health (NCCIH), saw palmetto has been used safely in studies lasting up to 3 years, and side effects are generally mild and infrequent, such as digestive upset, dizziness, or headache. NCCIH notes it does not appear to affect PSA readings, even at higher amounts, which is consistent with STEP and CAMUS. It may not be safe during pregnancy or breastfeeding.
Two caveats. First, “safe in trials” applies to the specific extracts that were tested, and products on store shelves can differ. Second, NCCIH advises talking with a health care provider before using any herbal product, because some herbs and medicines can interact. If you take a blood thinner or have a procedure coming up, mention any supplement you use.
So what should a man with urinary symptoms actually do?
The research does not say urinary symptoms are unimportant. It says this particular herb, taken alone, did not beat placebo in the best trials. Here is a practical approach:
- Get the symptoms evaluated first. Frequent urination, a weak stream, or nighttime trips can come from BPH, but also from diabetes, infections, medications, or sleep problems. Our prostate health hub explains the common patterns.
- Start with habits that have a clear rationale. The NIDDK suggests drinking less fluid before bed or before going out, limiting alcohol and caffeine, staying active, and not holding urine for long periods (NIDDK). Our page on nighttime urination covers more everyday factors.
- Review your medicines. NIDDK lists decongestants, antihistamines, some antidepressants, tranquilizers, and diuretics among medicines that can affect urinary symptoms. Do not stop a prescription on your own; ask whether timing or alternatives make sense.
- Know that proven treatments exist. Prescription medicines and procedures for BPH have been tested in large trials. A urologist or primary care clinician can match options to how much your symptoms bother you.
- If you still want to try saw palmetto, set realistic expectations, tell your clinician, and do not use it to delay an evaluation. Keep in mind that improvement over a few months could be the same natural fluctuation seen in the placebo groups.
Other ingredients are marketed for prostate comfort too, such as stinging nettle (often combined with saw palmetto) and zinc. The Cochrane reviewers rated combination products as uncertain rather than proven. For a side-by-side look at how strong the evidence is for each, see our best-researched ingredients for prostate health guide, and our prostate supplement guide compares products if you are weighing options.
When should you talk to a doctor?
See a health care professional about any new or changing urinary symptoms, and especially before starting a supplement for them. NIDDK advises getting care right away if you:
- Cannot urinate at all
- Have painful, frequent, urgent urination with fever and chills
- See blood in your urine
- Have severe discomfort or pain in the lower abdomen or urinary tract
Urinary symptoms are not a sign of prostate cancer in most men, but they deserve an evaluation. If PSA testing comes up in that conversation, our page on prostate checkups and PSA questions cover what to ask.
