Viagra drug structure formulae - stock illustration

Viagra. Structure formulae of the drug Viagra sildenafil. The drug is used to treat male impotence. The atoms represented as cylinders are colour-coded: carbon (green), hydrogen (white), nitrogen (blue), oxygen (red), sulphur (yellow). Unlike treatments that directly cause penile erections, Viagra affects the response to sexual stimulation. Viagra enhances the smooth muscle relaxant effects of nitric oxide, which is released in response to sexual stimulation. Smooth muscle relaxation allows blood to enter the penis leading to an erection.