Saw Palmetto

What it is

Saw palmetto is the extract of the berry of the American dwarf palm, Serenoa repens, which is used as a herbal treatment for urinary symptoms of benign prostatic hyperplasia (BPH), an enlarged prostate [1].

What the research says

Versus placebo. In the CAMUS trial of 369 men aged 45 or older, symptom scores fell by 2.20 points with saw palmetto (one, two and then three doses, where a dose was 320 mg a day, over 72 weeks) and by 2.99 points with placebo, a 0.79-point difference favouring placebo; it was no better than placebo on any secondary outcome [2]. A Cochrane review of 32 randomized trials (5,666 men, 4 to 72 weeks) found that in two high-quality long-term trials (582 men) saw palmetto was not superior to placebo (mean difference 0.25 points, 95% CI -0.58 to 1.07), and that it did not improve peak urine flow (0.40 mL/s, -0.30 to 1.09) or prostate size (-1.22 cc, -3.91 to 1.47) [1]. A 2021 meta-analysis of 27 trials (4,853 men) found little to no difference in urinary symptoms, quality of life or adverse events at short- and long-term follow-up [3]. A 2021 network meta-analysis of 22 trials (8,564 men) found no clinically meaningful improvement in symptoms or peak flow [4].

Versus tamsulosin. A meta-analysis of 4 studies (1,080 men) found saw palmetto and tamsulosin gave the same symptom score (mean difference 0.63, 95% CI -0.33 to 1.59), quality of life, peak flow and residual volume after at least 6 months, although tamsulosin reduced prostate volume more [5]. Ejaculation disorders (odds ratio 12.56, 3.83 to 41.18) and reduced libido (5.40, 1.17 to 24.87) were less common with saw palmetto [5].

Hexanic extract. A 2018 meta-analysis of randomized trials and observational studies of the hexanic extract (Permixon) found 0.64 fewer voids a night (95% CI 0.31 to 0.98 fewer) and a 2.75 mL/s higher peak flow (0.57 to 4.93) than placebo, similar symptom scores to tamsulosin and to 5-alpha-reductase inhibitors at 6 months, no negative effect on sexual function or PSA, and a mean incidence of gastrointestinal side effects of 3.8% [6].

Sexual function. A 2021 meta-analysis of 20 papers found no statistically significant negative effect of saw palmetto on sexual function compared with placebo or tamsulosin, with high heterogeneity [7].

Doses used in studies

The CAMUS trial gave one dose of saw palmetto extract (320 mg a day), then two and three doses at 24 and 48 weeks [2]. The Cochrane review included trials of 4 to 72 weeks [1].

Safety and interactions

Common side effects. A systematic review of 40 articles found side effects mild and similar to placebo, most often abdominal pain, diarrhoea, nausea, fatigue, headache, decreased libido and rhinitis [8]. The hexanic extract meta-analysis reported gastrointestinal side effects in 3.8% [6].

Upper limits and toxic doses. The CAMUS trial increased the dose to three times the starting dose with no clearly attributable adverse effects [2]. More serious events such as death and cerebral haemorrhage appeared only in isolated case reports and spontaneous reports, and causality is questionable [8].

Interactions. No drug interactions were reported in the safety review [8].

Pregnancy and breastfeeding. No data were found in the studies reviewed.

Relevant conditions. Urinary symptoms can have causes other than BPH, so men should have them checked by a doctor; PSA was not negatively affected in the hexanic extract analysis [6].

Caveats and open questions

The evidence is split by extract type: high-quality trials of standard extracts found no benefit, while the hexanic extract analysis included observational studies [2][1][6]. Similar scores to tamsulosin do not by themselves show a benefit over placebo, because the placebo group also improved in CAMUS [5][2]. The sexual function analysis showed high heterogeneity [7].