herb · for overactive bladder
Saw Palmetto
Proposed to act on the nerve receptors that trigger a bladder squeeze.
Say that in clinical terms
Proposed binding to muscarinic receptors and inhibition of vanilloid (TRPV1) receptors on bladder afferent nerves, which could theoretically calm an overactive bladder — distinct from its proposed anti-androgen mechanism in the prostate.
How strong is the research?
2 papers read.
Tested as: Saw palmetto fruit extract, 320 mg/day for 12 weeks, in placebo-controlled trials run in Japanese adults (including a study restricted to women) with self-reported/possible LUTS — not a clinical OAB diagnosis by International Continence Society criteria.
Who was studied: Japanese adults over 50 with frequent and urgent urination, including a separate group of women.
We read the research behind this and none of it concluded that it works for this. That is a finding about the papers, not a verdict that it does nothing.
How much to take
320 mg
Before you take it
- No Tolerable Upper Intake Level (UL) has been established by NIH ODS for saw palmetto (Serenoa repens) — it is a botanical extract, not a nutrient with a defined UL.
- Contraindicated in pregnancy and lactation: 5-alpha reductase (5-AR) inhibition may disrupt androgen-dependent fetal development; saw palmetto is effectively Category X in pregnancy.
- Case reports document increased bleeding risk in patients co-administering anticoagulants (warfarin) or antiplatelet agents; the proposed mechanism is antiplatelet activity from fatty acid constituents. Clinical significance is debated but co-administration warrants caution.
- May reduce efficacy of exogenous hormonal therapies — including oral contraceptives, testosterone replacement, HRT, and co-prescribed anti-androgens (spironolactone, cyproterone) — by competing for the same androgenic pathway.
- 5-AR inhibition suppresses PSA values; men taking saw palmetto may show false-low PSA results, potentially obscuring early prostate cancer detection.
- Rare case reports of cholestatic hepatitis have been associated with saw palmetto; the causal relationship is unconfirmed but hepatotoxicity is a recognized rare adverse event.
- Most common adverse effects are GI-related (nausea, diarrhea, constipation, abdominal discomfort); generally mild and transient at standard doses.
- In vitro inhibition of CYP2C9, CYP2C19, and CYP3A4 has been observed at supratherapeutic concentrations; no clinically confirmed pharmacokinetic drug-drug interactions have been demonstrated at standard doses (160–320 mg/day).
When to take it
Best taken: with food