Does saw palmetto shrink the prostate?

The evidence does not support that. The CAMUS trial, the largest and best-designed study, found no improvement in urinary symptom scores over placebo even at triple the standard dose. Earlier smaller studies were more positive, and the discrepancy is best explained by their methodological limits.

Does saw palmetto affect a PSA test?

It can. Saw palmetto may lower measured PSA, which risks masking a reading your doctor would otherwise act on. Anyone being monitored for prostate health should tell their doctor they are taking it.

Why is saw palmetto in so many supplements?

Familiarity and category convention rather than strength of evidence. It is the best-known prostate botanical, inexpensive, and customers expect to see it, so it appears in blends whose purpose has little to do with urinary symptoms.

Is saw palmetto safe?

It is generally well tolerated. Reported side effects are mild and mostly digestive. The two practical cautions are its effect on PSA readings and a theoretical interaction with blood-thinning medication.

Saw Palmetto and the Prostate: A Mixed Record

Horsaewood Editorial Team
Independent supplement research · Updated 5 August 2026

8 min read · 5 cited sources

Quick Answer: Does Saw Palmetto Work?

For urinary symptoms, probably not. The CAMUS trial — 369 men, randomised, placebo-controlled, running up to triple the usual dose for 72 weeks — found no meaningful improvement over placebo. Earlier, smaller studies were positive, and the most likely explanation is that they were less rigorous rather than that the larger trial missed something. For male vitality specifically, there is essentially no direct evidence; saw palmetto is a prostate ingredient that ended up in vitality blends by convention.

Best evidence: the CAMUS trial, and it was negative.
Typical dose: 320 mg daily of a lipidosterolic extract.
Practical caution: it can lower a PSA reading.

Man outdoors in natural daylight — Saw palmetto is among the most widely sold botanicals for men — and among the most thoroughly tested, which is why its record is so clear.

What it is, and why it became popular

Serenoa repens is a fan palm native to the south-eastern United States. Its berries have been used for urinary complaints since long before anyone measured prostate volume, and the modern supplement is a lipidosterolic extract standardised to roughly 85–95% fatty acids and sterols.

The proposed mechanism is inhibition of 5-alpha reductase, the enzyme converting testosterone into dihydrotestosterone — the same target as the prescription drug finasteride. That is a coherent story, and it is the reason saw palmetto was taken seriously enough to be tested properly.

The trial that settled it

The Complementary and Alternative Medicine for Urological Symptoms study, published in JAMA in 2011, is the one that matters. It randomised 369 men with lower urinary tract symptoms to saw palmetto or placebo, and escalated the dose from 320 mg to 640 mg and then 960 mg per day over 72 weeks.

The result was flat. There was no significant difference in symptom scores at any dose, including triple the amount sold in most supplements. A Cochrane review reached the same conclusion across the wider literature: the more rigorous the study, the smaller the effect.

Outcome	Evidence quality	Honest summary
Urinary symptoms (BPH)	Good — and negative	Large randomised trial found no benefit over placebo
Prostate volume	Weak	No consistent effect demonstrated
Male vitality / libido	Insufficient	Not what it was studied for
Hair loss	Very limited	A few small studies, not comparable to finasteride
Tolerability	Good	Consistently well tolerated across trials

So why is it in almost every blend?

Because it is expected. Saw palmetto is the botanical men recognise when they think about prostate health, it is inexpensive, and its absence from an ingredient list is more likely to cost a sale than its weak evidence is. That is a commercial reason, not a scientific one, and it is worth naming plainly.

Its presence in a formula is not a mark against that formula. It is simply not a reason to choose one — and if a product's case rests mainly on containing saw palmetto, that case is weaker than it sounds.

The PSA problem

This is the practical point worth carrying away. Saw palmetto can lower measured prostate-specific antigen. If you are being monitored, a suppressed reading could mask a change your doctor would otherwise investigate.

It is not a reason to avoid it. It is a reason to mention it at your next appointment, in the same way you would mention any other supplement.

What this means in practice

If you are taking a blended formula that happens to contain saw palmetto, there is no cause for concern — it is safe and well tolerated. If you are buying a supplement specifically to improve urinary symptoms, the evidence does not support that choice, and a urologist is a better use of the money. And whichever applies, tell your doctor, because of the PSA effect.

How Horsewood uses saw palmetto

It is one of seven botanicals in the formula. See where the evidence is stronger — and where it is not.

Read the Full Review

References

Barry MJ et al. Effect of increasing doses of saw palmetto extract on lower urinary tract symptoms: the CAMUS randomized trial. JAMA, 2011.
Tacklind J et al. Serenoa repens for benign prostatic hyperplasia. Cochrane Database of Systematic Reviews, 2012.
Bent S et al. Saw palmetto for benign prostatic hyperplasia. N Engl J Med, 2006.
Habib FK, Wyllie MG. Not all brands are created equal: a comparison of selected components of different brands of Serenoa repens extract. Prostate Cancer Prostatic Dis, 2004.
Andriole GL et al. Dietary supplements and PSA interpretation. Urology, 2005.