Viagra relaxes muscles within the penis. This allows increased blood flow into the penis, necessary to achieve and maintain an erection.

Viagra is used to treat erectile dysfunction (impotence).

Viagra may also be used for purposes other than those listed in this medication guide.

• Take Viagra exactly as directed by your doctor. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.
• Take each dose with a full glass of water.
• Viagra is usually taken when needed. It can be taken anywhere from 4 hours to one-half hour before sexual activity. Generally, it is taken 1 hour before sexual activity. The medication can help achieve an erection when sexual stimulation occurs. An erection will not occur just by taking a pill. Follow your doctor's instructions.
• Taking Viagra after eating a high-fat meal (such as a cheeseburger and french fries) may cause the medication to take a little longer to start working.
• Do not take Viagra more than once a day.
• If you develop dizziness, nausea, or angina (pain, tightness, discomfort, numbness, or tingling in the chest, arms, neck, or jaw) during sexual activity, refrain from further sexual activity and notify your doctor.
• Contact your doctor or seek emergency medical attention for any erection that lasts longer than 4 hours. A sustained erection can damage the penis.
• Grapefruit and grapefruit juice may interact with Viagra. The interaction could lead to potentially adverse effects. You should discuss the use of grapefruit and grapefruit juice with your doctor. Do not increase or decrease the amount of grapefruit products in your diet without first talking to your doctor.
• Store this medication at room temperature away from moisture and heat.