(See also Overview of Dietary Supplements.)
Saw palmetto (Serenoa repens, Serenoa serrulata) berries contain the plant’s active ingredients. The active ingredients, thought to be fatty acids, seem to inhibit 5-alpha-reductase, thus opposing the conversion of testosterone to dihydrotestosterone. The berries can be used to make a tea, or they can be extracted into tablets, capsules, or a liquid preparation. Most formulations evaluated in clinical studies are hexane extracts of saw palmetto berries, which are 80 to 90% essential fatty acids and phytosterols.
There is no scientific evidence to suggest that saw palmetto reverses BPH. A double-blind, multicenter, placebo-controlled randomized trial of 369 men found that increasing doses of a saw palmetto fruit extract did not reduce lower urinary tract symptoms more than placebo (1). In addition, a 2012 Cochrane review of 32 randomized, controlled trials, determined that saw palmetto, at double and triple doses, did not improve urinary flow measures or prostate size in men with lower urinary tract symptoms consistent with BPH (2). Claims that saw palmetto increases sperm production, breast size, or sexual vigor are unsupported.
Headache and diarrhea may occur, but few serious adverse effects have been reported. One case report of a 58-yr-old white man taking 900 mg of dried extract and 660 mg of berry powder to ease the symptoms of BPH reported acute liver damage due to saw palmetto (3). Another report of a 65-yr-old male indicated that supplementation with saw palmetto may have been responsible for acute pancreatitis (4).
Saw palmetto may interact with estrogens; thus, women who are pregnant or who may become pregnant should not take it.
No interactions have been reported for saw palmetto (5); however, although strong evidence is not available, patients on warfarin should be careful when considering or taking saw palmetto because of a possible risk of hepatotoxicity.
Barry MJ, Meleth S, Lee JY, et al; Complementary and Alternative Medicine for Urological Symptoms (CAMUS) Study Group. Effect of increasing doses of saw palmetto extract on lower urinary tract symptoms: a randomized trial. JAMA 306(12):1344-1351, 2011.
Tacklind J, Macdonald R, Rutks I, et al.Serenoa repens for benign prostatic hyperplasia. Cochrane Database Syst Rev 12:CD001423, 2012.
Lapi F, Gallo E, Giocaliere E, et al. Acute liver damage due to Serenoa repens: a case report. Br J Clin Pharmacol 69(5):558-560, 2010.
Wargo KA, Allman E, Ibrahim F. A possible case of saw palmetto-induced pancreatitis. South Med J 103(7):683-685, 2010.
Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: an updated systematic review. Drugs 69(13):1777-1798, 2009.