What Is Saw Palmetto?
Saw palmetto (Serenoa repens) is a small palm native to the southeastern United States. Its berry extract has been used for centuries in traditional medicine for urinary complaints and is now one of the best-selling herbal supplements globally. It is categorised as a dietary supplement in the US and a phytomedicine in several European countries.
Quick Facts
- Botanical name: Serenoa repens (syn. Sabal serrulata)
- Plant part used: Berry (fruit extract)
- Active compounds: Fatty acids, phytosterols, polysaccharides
- Primary proposed mechanism: 5-alpha reductase inhibition, anti-inflammatory
- Clinical doses in trials: 160 to 320 mg/day of lipophilic extract
- Evidence quality: Multiple RCTs and meta-analyses; results mixed but positive overall
How Saw Palmetto Is Proposed to Work
The primary mechanisms proposed for saw palmetto's prostate benefits are: (1) mild inhibition of 5-alpha reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT). DHT is the androgen most responsible for prostate cell growth, so reducing its formation may slow BPH progression. (2) Anti-inflammatory effects on prostate and bladder tissue, reducing smooth muscle spasm and urgency signals. (3) Possible alpha-adrenergic blocking activity, relaxing the smooth muscle of the bladder neck and prostate, similar to the mechanism of tamsulosin.
Summary of Clinical Evidence
The evidence base for saw palmetto is one of the most studied in the herbal supplement field, and also one of the most debated. Key findings include:
- A 2009 Cochrane review of 30 trials found saw palmetto was associated with small to moderate improvements in LUTS symptoms compared to placebo
- A landmark 2011 NEJM study (STEP study) found no significant difference between saw palmetto and placebo over 72 weeks in men with moderate-to-severe LUTS
- A 2013 follow-up study at triple the dose also found no significant benefit over placebo
- Multiple older meta-analyses found improvements in peak urine flow, nocturia, and LUTS scores
- Studies using higher-quality, standardised extracts tend to show more consistent benefit than those using lower-quality preparations
The overall picture is that saw palmetto may benefit some men, particularly those with mild to moderate BPH, when using a standardised lipophilic extract at an adequate dose. Effect sizes are modest compared to pharmaceutical 5-ARI drugs, but the side effect profile is also much more favourable.
Saw Palmetto and Nocturia
Several trials have specifically found saw palmetto associated with reduced nocturia (nighttime urination frequency). While this finding is not universal across all studies, it is one of the most commonly reported benefits in positive trials, which aligns with patient-reported outcomes in real-world use.
Saw Palmetto and Urine Flow
Peak urine flow rate improvements have been reported in several saw palmetto trials. The proposed mechanism of bladder neck smooth muscle relaxation and reduced DHT-driven prostate tissue pressure is biologically plausible for this outcome. Effect sizes tend to be modest but clinically relevant for men with mild BPH.
Saw Palmetto Safety Profile
Saw palmetto is generally very well tolerated. Reported side effects are infrequent and typically mild (occasional nausea or mild digestive discomfort). A notable interaction risk is with anticoagulant medications: saw palmetto has mild antiplatelet activity and may potentiate the blood-thinning effects of warfarin or aspirin. Men on blood thinners should consult their physician before use.
Saw Palmetto in ViriFlow
ViriFlow includes saw palmetto as one of its two primary botanical ingredients within a 700 mg proprietary blend. The extract is provided as a 1:5 concentration. The individual saw palmetto dose within the blend is not disclosed. For the full ingredient context, see ViriFlow's ingredient breakdown. For the overall evidence review, see does ViriFlow work.
Saw Palmetto Benefits Summary
- Mild 5-alpha reductase inhibition reduces DHT-driven prostate growth
- Anti-inflammatory effects on prostate and bladder smooth muscle
- Evidence for modest improvements in LUTS, nocturia, and peak urine flow in some trials
- Evidence is mixed across high-quality RCTs; benefits most consistent in mild-to-moderate BPH
- Well-tolerated safety profile with mild side effects
- Mild anticoagulant activity: interaction risk with blood thinners
- Part of ViriFlow's primary botanical ingredient pair alongside pygeum