Because many men choose to take saw palmetto extracts, the potential adverse effects of this dietary supplement must be ascertained so that these individuals can make informed decisions about their use of this product. The STEP study provided a unique opportunity to make detailed assessments about potential toxicities of saw palmetto, having obtained extensive data on both symptomatic side effects as well as asymptomatic laboratory abnormalities and included a placebo group which allowed for comparison with an untreated control condition.
Overall, we found no evidence that consumption of this saw palmetto extract, at a dose of 160mg twice daily over a period of one year, was associated with any clinically important adverse effects. Relatively few participants suffered serious adverse events, and these were more common in the placebo-allocated participants. Non-serious adverse events were nearly equally distributed between the saw palmetto and placebo groups, both in total number and in the proportion of participants who suffered at least one adverse event. Only one of the five domains on the O’Leary sexual-functioning instrument (the perception-of-problems domain) showed a significant difference between treatment groups; however, this difference was small (approximately 1/3 of a point difference on a 12-point scale). Finally, we found little evidence of toxicity of saw palmetto among the laboratory analyses performed: while there were a small number of significant results, the large number of tests conducted would be expected to generate a small number of significant differences due to chance. Further evidence suggesting that these differences are most likely due to chance is the fact that no other liver-function tests besides the total bilirubin showed significant differences and that the greater source of the observed difference in potassium levels was due to a small decline in the placebo group, not a rise in the saw palmetto group (); the significant difference in glycosuria was due to an increase in urine glucose in placebo-allocated participants. Recent laboratory evidence also suggests that saw palmetto does not have serious hepatic toxicity (21
With the growing popularity of dietary supplements, it is imperative that better data on their potential toxicities be generated. Several dietary supplements have been shown to have serious toxic effects and have been removed from the market in the U.S. and some European countries. There is a compelling need to better understand potential adverse effects of other widely used dietary supplements, so that consumers can make more informed decisions about risks and benefits.
The efficacy of saw palmetto extracts for the treatment of BPH is still a matter of controversy and higher-quality studies of this phytotherapeutic are now beginning to appear. Regardless of the ultimate outcomes of these studies, saw palmetto extracts will likely continue to be used widely by men who feel that they benefit from its use (22
). Prior studies suggested that side effects of saw palmetto may include headache, dizziness, nausea, and constipation but assessment of adverse effects of saw palmetto has often been incomplete and unsystematic (23
). The STEP trial data are reassuring in that no important toxicities of this extract were identified among the group of patients studied.
These reassuring results, however, must be viewed within the context of the study limitations. The statistical power to detect important clinical differences was limited for some variables, given the sample size of the study. The follow-up phase was one year, so no conclusions regarding use over a longer time period can be made. Whether the favorable safety profile of the extract used in this study is typical of other extracts cannot be determined, as there is variation in the extraction techniques and final product composition among the marketed products (24
). Finally, rare but serious adverse effects of saw palmetto cannot be assessed in a trial of this size and, like pharmaceutical agents, will require large-scale post-marketing studies to adequately assess this possibility. While case reports do not establish causality, there are case reports suggesting that serious idiosyncratic toxicity of saw palmetto may exist: one patient developed cholestasis after taking an herbal blend that contained saw palmetto (25
), another developed transient hepatitis and pancreatitis (26
), and one patient suffered excessive intra-operative bleeding and prolonged bleeding time from saw palmetto (27
Overall, the data from the STEP trial do not support the concern of serious clinical adverse effects of this saw palmetto extract over a period of one year. While these results are reassuring, further data are needed to more definitively address toxicity issues and will likely emerge from ongoing investigations of saw palmetto as well as population-based toxicity studies.