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Anti-impotence pills. Blister packs of Magnus, a generic form of Viagra, the first oral treatment for male impotence. Viagra is the trade name for the drug sildenafil citrate. It is used to treat erectile dysfunction. Sildenafil citrate enhances the smooth muscle relaxant effects of nitric oxide, a chemical that is released in response to sexual stimulation. Relaxation of the smooth muscle allows blood to enter the penis, resulting in an erection. (KEYSTONE/SCIENCE PHOTO LIBRARY/STEVE PERCIVAL)