Saw palmetto (Serenoa repens) is a dwarf American palm native to the extreme southeastern United States. A lipidosterolic extract of its berries contains fatty acids (especially lauric acid), phytosterols, monocylglycerides, and polysaccharides. Fatty acids constitute more than 80% of the extract and are thought to be the most clin-ically effective component. It is widely used to treat be-nign prostatic hypertrophy (BPH). The berries them-selves are less well absorbed than the extract and are therefore believed to be less effective.
Saw palmetto extract can inhibit the enzyme 5- -reductase in vitro. This enzyme converts testosterone into dihy-drotestosterone (DHT), which in turn contributes to prostatic enlargement. Saw palmetto also appears to have an antiinflammatory effect and can reduce DHT binding to prostatic androgen receptors (antiandrogenic effect). Despite its proposed 5- -reductase mechanism, saw palmetto has not consistently lowered serum testos-terone, DHT, or prostate-specific antigen (PSA) levels, so it is likely that other mechanisms exist. While several earlier studies did indicate lowered PSA levels, more re-cent research has not supported these findings. It ap-pears that saw palmetto does not shrink the total prostate either, although it may reduce the size of the transition zone or inner prostatic epithelium.
Numerous (but not all) trials have indicated improve-ment in BPH symptom scores compared to placebo with 1 to 3 months of therapy. Saw palmetto extract ap-pears to be equally effective as finasteride but is less effective than α1-adrenoceptor antago-nists. No information appears to be available on the use of saw palmetto in the prevention of hair loss.
Headache and GI symptoms are the most frequently re-ported side effects. It is possible to reduce GI side ef-fects, such as nausea, abdominal discomfort, and diar-rhea, by taking the extract with food. Theoretically, decreased libido or erectile dysfunction could also oc-cur. Because of saw palmetto’s possible hormonal ef-fects (and lack of indications for use), pregnant and nursing women should avoid it. It is important to rule out prostate cancer in those taking saw palmetto for BPH, since the symptoms are similar. The effect of saw palmetto on prostatic cancer would likely be beneficial but not curative. No drug interactions have been re-ported.
For BPH, 320 mg of the lipidosterolic extract by mouth daily in two divided doses with food is usually recom-mended. It must be taken for a minimum of 3 months and perhaps indefinitely. The dried berries and tea are not recommended, since the fatty acids responsible for clinical effect would be largely lost.
Saw palmetto extract is a fairly well tolerated, safe al-ternative to finasteride for long-term treatment of BPH, although α1-adrenoceptor blocking agents undoubtedly afford more rapid symptom relief.
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