Saw palmetto extract
Saw palmetto extract is an extract of the fruit of Serenoa repens.  It is rich in fatty acids and phytosterols, and has been shown to be effective in the management of benign prostatic hyperplasia.
Native Americans used the fruit for food, but also in the treatment of a variety of urinary and reproductive system problems. The European colonists learned of the use of saw palmetto. It was used as a crude extract for at least 200 years for various conditions including asthenia (weakness), recovery from major illness, and urogenital problems. For instance, the Eclectic physician H. W. Felter wrote of it, "Saw palmetto is a nerve sedative, expectorant, and a nutritive tonic, acting kindly upon the digestive tract...Its most direct action appears to be upon the reproductive organs when undergoing waste of tissue..."
The Eclectics knew saw palmetto as more than a prostate herb.  King's American Dispensatory, in 1898 claims:
It is also an expectorant, and controls irritation of mucous tissues. It has proved useful in irritative cough, chronic bronchial coughs, whooping-cough, laryngitis, acute and chronic, acute catarrh, asthma, tubercular laryngitis, and in the cough of phthisis pulmonalis. Upon the digestive organs it acts kindly, improving the appetite, digestion, and assimilation. However, its most pronounced effects appear to be those exerted upon the urino-genital tracts of both male and female, and upon all the organs concerned in reproduction. It is said to enlarge wasted organs, as the breasts, ovaries, and testicles, while the paradoxical claim is also made that it reduces hypertrophy of the prostate. Possibly this may be explained by claiming that it tends toward the production of a normal condition, reducing parts when unhealthily enlarged, and increasing them when atrophied.
In modern times, much research has been done on extract made from the fruits, which are highly enriched with fatty acids and phytosterols. This research has been the subject of a thorough meta-analysis published in the Journal of the American Medical Association and has been shown to be effective for the treatment of men with symptomatic benign prostatic hyperplasia (enlargement of the prostate) compared to placebo and the two major categories of drugs used for men with this condition. There are also small, positive clinical trials published on the use of saw palmetto extracts topically and internally for male-pattern baldness. In 2005, a long-term, placebo-controlled trial showed that a combination of saw palmetto fruit and nettle root extracts were effective in treating urinary tract symptoms in older men. However, in February 2006, a large, blinded placebo-controlled study published in the New England Journal of Medicine showed no reduction of symptoms from enlarged prostate by taking saw palmetto, as compared to placebo. Designers of the latest study questioned whether the differently-flavored placebos in previous studies were adequately blinded. Critics of the latest study questioned whether a sufficient dosage of active ingredients was given. An earlier single case study on saw palmetto concluded that searching for information on a herbal medicine using MEDLINE alone was insufficient, and expanded their search to "alternative" databases, including AGRICOLA, EMBASE, IBIS, and Cochrane, plus a manual search of unindexed herbal journals.
Other research has shown that the herb works by multiple mechanisms, including inhibiting 5-alpha-reductase, interfering with dihydrotestosterone binding to the androgen receptor, by relaxing smooth muscle tissue similarly to alpha antagonist drugs, and possibly by acting as a phytoestrogen.
Because the fruit is the part used and because a prolific quantity is produced by an adult saw palmetto plant, this herbal medicine is considered ecologically sustainable.
Though in vitro studies suggest saw palmetto has properties that might make it useful against prostate cancer cells or to reduce prostatitis, clinical trials are lacking.
David Winston RH (AHG) describes a variety of conditions where saw palmetto extract is useful for men and women, using both research and ethnobotanical uses.  

# Contraindications and side effects
Though men taking saw palmetto may develop mild nausea, reduced libido, or erectile dysfunction, the rate of such problems is clinically and statistically far less common than in men taking drugs to treat BPH symptoms, based on the JAMA meta-analysis cited above. There are no known drug interactions. It should generally be avoided in pregnancy and lactation and in small children due to lack of experience and knowledge in these populations and because of the purely theoretical risk of hormonal interference.
While saw palmetto is generally considered safe, one of its primary active ingredients, beta-sitosterol, is chemically similar to cholesterol. High levels of sitosterol concentrations in blood have been correlated with increased severity of heart disease in men who have previously suffered from heart attacks.
For some people, an increase in libido has been reported through usage. As with other nutrients and herbs, various people will have different responses based on their chemical and biological make up.