First brought to market in 1998, Viagra is the “little blue pill” that transformed the face of erectile dysfunction treatment, offering a way for impotent men to resume sexual activity. Like the other PDE5 inhibitors on the market, Viagra’s active ingredient, sildenafil citrate, temporarily blocks the effects of the phosphodiesterase-5 enzyme that impedes blood flow to the penis and can make it difficult to get an erection.
Available in strengths ranging from 25 milligrams to 100 milligrams, Viagra is designed to be taken roughly an hour before sexual activity and usually lasts for four hours or so. Doctors usually start patients on a 50-milligram dose, adjusting it upward or downward based on the patient’s reaction. No more than a single dose should be taken in any 24-hour period. Because Viagra lowers blood pressure, it should never be taken at the same time as any nitrate-based drugs, such as nitroglycerin, widely prescribed to treat angina.