Saw Palmetto

Saw palmetto seems to inhibit male hormones by reducing the conversion of testosterone to dihydrotestosterone (DHT), which stimulates prostate growth. Exactly how the saw palmetto exerts this influence when taken in extract form is not known.

Saw palmetto has been used in Europe as a prescription product called Permixon. Saw palmetto is available in the U.S., as a supplement -- not a medication.

The recommended dose for saw palmetto is 320 mg of extract per day. The amount used in most studies is usually divided into two, 160-mg doses.

Scientific Evidence
Saw palmetto is by far the most studied of the plant medicines used for BPH and has the most evidence to support its use. Most studies come from Europe where saw palmetto has been a standard, drug therapy for 20 years as the prescription product, Permixon.

• One study -- involving more than 1,000 men who were randomly given either Permixon or finasteride (Proscar®), an enzyme inhibitor commonly prescribed in the U.S. -- found that both treatments relieved urinary symptoms in about two-thirds of the men. The study also found that Permixon had fewer adverse effects than finasteride, especially on sexual function and desire. But the size of the prostate was reduced more in men who took finasteride than in men who took saw palmetto. The men had similar positive effects on symptom scores (–37% for Permixon versus –39% for finasteride) and peak urinary flow rates (+25% versus +30%). Finasteride reduced prostate volume and PSA levels, but Permixon had no effect on these.

  One notable problem with this study was that it did not include a placebo group, so it was impossible to know whether the positive effect on the men was simply the result of the placebo. (Generally, about 40% to 50% of men on placebo therapy show improvement in their symptoms and urinary flow rate.)

• A recent review of 18 randomized studies (involving 2,939 men) attempted to combine the results of the best studies that compared saw palmetto with a placebo. The researchers found that about three-quarters of the men who took saw palmetto but just one-half of the men taking a placebo reported improved symptoms. For the men who took saw palmetto, symptom scores were reduced by 28%, frequency of nighttime urination was 25% lower, peak flows were 24% greater, and the amount of urine left in the bladder after urination was reduced by 43%.

  Still, the review has limited value because the studies took place over a short duration (averaging nine weeks), used a variety of saw palmetto preparations and measured outcomes differently.

• Another review of the available evidence included only placebo-controlled studies that used Permixon. The analysis of 13 trials involving 2,859 men treated with Permixon showed that peak urinary flow rates improved by nearly 2 ml/sec and the frequency of getting up at night to urinate was reduced by 0.55 times per night (one trip less every two nights) for men taking Permixon versus men who took placebos. But both the placebo group and the Permixon group gave the same assessment of the effectiveness of the treatment that they received -- showing the power of the placebo again.

This review also was limited because the small studies used did not last very long.