We could combine them in a cocktail, some to work in the brain and some to work locally, for the best effect. Patients who have tried the experimental pills say they work easily. Between 10 million and 20 million American men suffer impotence at some point in their lives. Impotence increases with age, and some 80 percent is caused by disease, particularly diabetes and heart conditions that restrict blood flow, said Dr. Irwin Goldstein of Boston University.
Impotence also can be psychological or a side effect of certain drugs.
Pfizer Inc.'s Viagra, or sildenafil, blocks an enzyme found mainly in the penis that breaks down a chemical produced during sexual stimulation. The longer that chemical, called cyclic GMP, stays around, the better chance of an erection. In clinical studies of several thousand men, Viagra helped about 80 percent, said Padma-Nathan, who helped test all three drugs. The Food and Drug Administration last week promised a quick review of Viagra, meaning it could be sold by April. Unlike injection drugs, Viagra doesn't cause erections unless the man is sexually stimulated.