Saw Palmetto for Prostate: Three Cochrane Reviews Say No

Saw palmetto (Serenoa repens) berry extract is one of the most widely used herbal products for the urinary symptoms of benign prostatic hyperplasia (BPH) — the non-cancerous enlargement of the prostate that becomes increasingly common in men over 50. Industry analysts have estimated global saw palmetto sales in the hundreds of millions of dollars annually. Three successive Cochrane systematic reviews (Wilt et al. 2002, MacDonald et al. 2009, Tacklind et al. 2012), spanning two decades of cumulative randomized trial evidence, have consistently found that saw palmetto is no more effective than placebo for BPH symptoms. This is a story about how early encouraging data, a plausible mechanism, and strong commercial interests can sustain a market that better-quality science has steadily undermined.

The Initial Promise

Small trials from the 1980s and 1990s reported statistically significant improvements in urinary flow and symptom scores with saw palmetto in men with BPH. The proposed mechanism — modest inhibition of 5-alpha-reductase, the enzyme that converts testosterone to DHT (the hormone that drives prostate growth) — sounded biologically plausible, since prescription 5-alpha-reductase inhibitors like finasteride do reduce BPH symptoms. These early positive signals drove the adoption of saw palmetto as a mainstream "men's health" supplement.

What the Cochrane Reviews Found

The first Cochrane review (Wilt et al. 2002) found a modest positive signal but flagged serious methodological problems with the available trials — short duration, small samples, weak blinding. As better-quality trials accumulated, the picture changed. The STEP trial (Bent et al. 2006, NEJM) — 225 men randomized to saw palmetto 160 mg twice daily or placebo for one year — found no difference between groups on AUA Symptom Index or urinary flow. The CAMUS trial (Barry et al. 2011, JAMA) — a 369-man, NCCAM/NIDDK-funded multi-centre study with escalating doses of standard, double, and triple the usual dose of saw palmetto extract over 72 weeks — found no improvement compared with placebo on the AUA Symptom Index or any secondary outcome (group difference 0.79 points favouring placebo, P = 0.91 in the saw palmetto direction). The 2012 Cochrane review (Tacklind et al.), pooling 32 RCTs in 5,666 men, concluded that saw palmetto, even at double and triple doses, did not improve urinary flow measures or prostate size. In short: no benefit on peak urinary flow rate, no benefit on symptom scores, no benefit at any dose tested.

Why Men Still Buy It

BPH symptoms fluctuate naturally, so many men feel better on a new pill simply because they happened to start it during a less-bad stretch — a textbook setup for placebo and regression-to-the-mean effects. The supplement industry has largely continued to market the 1990s mechanism story without surfacing the subsequent Cochrane conclusions. For men with symptomatic BPH, evidence-based options include alpha-blockers (tamsulosin, alfuzosin, silodosin), 5-alpha-reductase inhibitors (finasteride, dutasteride), combination therapy, and behavioural changes (timed voiding, evening fluid restriction, limiting alcohol and caffeine), all of which outperform saw palmetto in head-to-head and placebo-controlled trials.