An enlarged prostate can put pressure on the urethra - the tube through which urine passes - and irritate the bladder. Some BPH symptoms include a weak urinary stream, inability to completely empty the bladder and frequent nighttime trips to the bathroom.

Men who are bothered by such symptoms have several options for combating them, including the herbal product saw palmetto, according to Dr. Harvey B. Simon, an associate professor of medicine at Harvard Medical School in Boston and editor of the Harvard Men's Health Watch.

Extracts of the berries of saw palmetto, also known as the dwarf palm, are widely used in Europe as an antidote to BPH symptoms. Saw palmetto is also the best studied of the herbal products marketed for treating the condition, Simon told Reuters Health.

"It's the one with the greatest promise," he said.

In the current issue of the Harvard Men's Health Watch, Simon details some of the research that suggests saw palmetto may ease BPH symptoms. For instance, a review of 18 studies found that overall, saw palmetto cut nighttime urination and other BPH symptoms by about one-quarter. The studies, conducted mostly in Europe, included nearly 3,000 men between the ages of 40 and 88.

A key shortcoming of the research on saw palmetto, Simon said, is that most studies have been short. The 18 included in the review he cites lasted for 9 weeks, on average.

Exactly why saw palmetto may aid in BPH is not fully clear. Simon points out that animal and lab research suggests that the herb affects hormone receptors on prostate cells. And like certain prescription drugs for BPH - finasteride (Proscar) and dutasteride (Avodart) - saw palmetto appears to inhibit an enzyme that converts testosterone to the hormone dihydrotestosterone, which is believed to be involved in prostate enlargement.

There are other herbs purported to ease BPH symptoms, such as Pygeum africanum - extracted from the bark of the African plum tree - and extracts from Urtica dioica, the stinging nettle. But the evidence for these herbs is weaker than that for saw palmetto, according to Simon.

And while he said it seems "reasonable" for men with BPH symptoms to give saw palmetto a try, Simon advised against "trying one herb after another" in search of help, as several proven prescription medications are available.

It's also important that men not take it upon themselves to diagnose and treat BPH. A man with symptoms of the condition should first see a doctor to confirm BPH as the cause, according to Simon, and those who decide to try an herb need to let their doctors know.

Another caveat he noted is that herbs are not regulated as medication in the U.S., so consumers cannot be sure an herbal product contains what the label states.

Besides herbs and mainstream medications, there are also some basic behavioral changes that can combat BPH symptoms, according to Simon. Among them are: reducing fluid intake; limiting alcohol and caffeine, and avoiding them after about 3 p.m.; and never passing up a chance to use the bathroom, even when your bladder doesn't feel full.