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Marketed as a natural remedy for an enlarged prostate, saw palmetto is a top-selling dietary supplement. It's extracted from berries that grow on saw palmetto palm trees, which are native to the southeastern United States.

By one estimate, more than a third of all US adults who take supplements use saw palmetto specifically. Some evidence suggests that saw palmetto has anti-inflammatory properties, and its use as folk medicine dates back over a century.

But experts at Harvard say men should view its supposed benefits for prostate health skeptically. "Saw palmetto is unlikely to harm you, but it probably won't provide any major benefits either," says Dr. Heidi Rayala, an assistant professor of urology at Harvard Medical School and Beth Israel Deaconess Medical Center.

BPH and the potential effect of saw palmetto

It's common for men to develop an enlarged prostate, or benign prostatic hyperplasia (BPH), when they get older. BPH impedes urinary flow through the urethra, causing obstructive symptoms that can worsen with time.

Just how saw palmetto might act on the prostate to improve symptoms isn't entirely clear, however. Some evidence suggest it mimics the effects of certain drugs used for treating BPH, including 5-alpha reductase inhibitors such as finasteride (Proscar), which shrink the prostate gland.

In the US, no herbal supplement is approved as BPH treatment. The American Urological Association cautions that studies backing saw palmetto for treating enlarged prostates have numerous flaws, including short durations and a lack of placebo controls. Most of the supporting evidence comes from small studies paid for by companies that sell dietary supplements.

What do randomized clinical trials show?

The best-conducted research shows no benefits from saw palmetto for BPH. During , 225 men with moderate to severe BPH were treated with either a placebo or 160 milligrams (mg) of saw palmetto, taken twice daily for a year. The investigators detected no difference in outcomes, but they also acknowledged that doses tested in the study may have been too low to produce measurable effects.

So, during , researchers tested higher doses of saw palmetto ranging up to 320 mg given three times a day. Nearly 370 men ages 45 and older were randomized to treatment or placebo groups. After year and a half, men in both groups reported feeling either no worse or a little better. Remarkably, 40% of the placebo-treated men said symptoms had improved, suggesting the simple act of taking a pill could have something to do with the supplement's perceived benefits.

Dr. Michael Barry, a professor of medicine at Harvard Medical School, led the study. He urges men to consult with their doctors before trying saw palmetto, mainly to rule out other potential causes of urinary obstruction, which can include bladder or prostate cancer. And saw palmetto may interfere with the blood's clotting ability, making it risky for men who take blood thinners.

Recent results and comments

The latest evidence on saw palmetto and BPH comes from a of 27 placebo-controlled studies enrolling a combined 4,656 participants. Results published in 2024 showed no improvement in urinary symptoms or quality of life from taking saw palmetto (alone or with other herbal supplements) over durations ranging up to 17 months.

"If the ingredients in these herbal products worked well for urinary symptoms, drug companies would have already had them approved by the FDA as a medicine that insurance companies would have to cover," Dr. Rayala said. "It's okay to take them, but just be cautious about spending too much of your own money on these alternatives."

"It is easy to understand why so many find taking a naturally occurring supplement for treating urinary difficulties in middle age appealing," said Dr. Marc Garnick, the Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, and editor in chief of the Harvard Medical School Guide to Prostate Diseases. "However, evidence of effectiveness with saw palmetto is lacking, and its use for BPH and other common urinary symptoms without a full evaluation of the potential cause should be discouraged."