Viagra (generic: sildenafil) is a prescription medication used to treat men with erectile dysfunction (impotence). Viagra belongs to a group of drugs called phosphodiesterase (PDE) inhibitors which work by relaxing muscles and increasing blood flow to the penis during sexual stimulation.

This medication comes in tablet form and is taken one hour before sexual activity.

Common side effects of Viagra include headache, facial flushing, and upset stomach.