Natural Viagra? 'Horny Goat Weed' Shows Promise

In the new study, Mario Dell'Agli and colleagues point out that Viagra (sildenafil) and several other prescription drugs are now available for ED, or male impotence. ED affects an estimated 18 million men in the United States alone. Studies show, however, that these drugs may cause side effects such as headache, facial flushing, stomach upset, and visual disturbances.

To find better treatments, the scientists studied herbal extracts reputed to improve sexual performance. Scientists exposed the substances to an enzyme that controls blood flow to the penis and whose inhibition results in an erection.

Of the extracts tested, "horny goat weed" was the most potent inhibitor of the enzyme. By chemical modification of icariin, the active ingredient purified from the extract, the scientists obtained a derivative with activity similar to Viagra and a potential for fewer side effects because it targeted the protein more precisely than sildenafil.