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Chemistry
The active constituents in saw palmetto berries are not well defined. Phytosterols (eg, -sitosterol), aliphatic alcohols, polyprenic compounds, and flavonoids are all present. Marketed preparations are lipophilic extracts that contain 85–95% fatty acids and sterols.
Pharmacologic Effects
Saw palmetto is most often used in the treatment of benign prostatic hyperplasia. Enzymatic conversion of testosterone to dihydrotestosterone (DHT) by 5 -reductase is inhibited by saw palmetto in vitro. This effect is similar to that of finasteride, which is also used to treat the disorder(Chapter 40: The Gonadal Hormones & Inhibitors). In vitro, saw palmetto also inhibits the bindingof DHT to androgen receptors. Additional effects that have been observed in vitro include inhibition of prostatic growth factors, blockade of 1-adrenoceptors, and inhibition of inflammatory mediators produced by the 5-lipoxygenase pathway. The clinical pharmacology of saw palmetto is not well defined. One week of treatment in healthy volunteers failed to influence 5 -reductase activity, DHT concentration, or testosterone concentration. Six months of treatment in patients with benign prostatic hyperplasia also failed to affect prostate-specific antigen (PSA) levels, a marker that is typically reduced by enzymatic inhibition of 5 -reductase. In contrast, other researchers have reported a reduction in epidermal growth factor, DHT levels, and estrogen expression after three months of treatment in patients with benign prostatic hyperplasia. The largest clinical trial to date compared saw palmetto, 320 mg/d, with finasteride, 5 mg/d, in 1098 patients. At 6 months, overall symptom score, quality of life, and peak urinary flow were significantly improved for both groups. Finasteride was significantly better at reducing prostate volume (18% versus 6%, respectively). Adverse effects were comparable in both groups except for a significantly greater degree of sexual dysfunction in patients receiving finasteride versus saw palmetto. Shortcomings in the latter trial included lack of placebo control and failure to extend the study duration beyond 6 months.
In a systematic review of seven double-blind placebo-controlled trials, saw palmetto was found to be significantly more effective than placebo in reducing nocturnal urinary frequency (33–74% versus 13–39%, respectively), in reducing daytime urinary frequency (11–43% versus 1–29%, respectively), and in increasing peak urinary flow (26–50% versus 2–35%, respectively). A recent meta-analysis of randomized controlled trials also indicated a therapeutic advantage of saw palmetto over placebo in improving urologic symptoms and flow measures. Small comparative trials of saw palmetto versus -blockers showed greater symptomatic improvement with -blockers.
Adverse Effects
In the largest clinical trial conducted to date, adverse events reported with an incidence of 1–3% included hypertension, decreased libido, abdominal pain, impotence, back pain, urinary retention, and headache. In another large-scale trial, gastrointestinal upset was the most common side effect.
Retirado do Livro do Katzung.
Esse negócio de não ter efeito colateral é marketing.
