herb · for hair thinning
Saw Palmetto
Blocks the conversion of testosterone into DHT, the hormone behind pattern hair loss.
Say that in clinical terms
Inhibits 5-alpha reductase, reducing conversion of testosterone to DHT, the primary androgenic trigger of pattern hair loss.
How strong is the research?
1 paper read, 1 supporting.
Who was studied: Men only, with mild to moderate pattern hair loss. Women were not tested.
How much to take
daily
160–320 mg
Standardized to 85-95% fatty acids. Most effective for androgenic alopecia in men.
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).
- In men using saw palmetto for AGA, 5-AR inhibition reduces serum PSA levels; this is clinically distinct in this male population because it may produce false-negative PSA screening results and delay detection of early prostate cancer — a specific risk in men who are also in the age range for prostate cancer surveillance.
When to take it
Best taken: with food
What we make of it
No placebo group. It was compared against a drug, so we cannot tell if it beat nothing.
The detail
The trial was open-label with two arms and no placebo — saw palmetto against finasteride. That means the 38% who responded cannot be credited to the supplement rather than to time, attention or expectation. The study was not designed to answer whether it beats doing nothing.