Viagra may cause side effects, but many people have slight side effects or none at all. Check with your doctor if any of these most common side effects of Viagra persist or become bothersome:

Back pain, diarrhea, dizziness, flushing, headache, indigestion, joint pain, lightheadedness, nasal stuffiness, vision changes (e.g. blurred vision, sensitivity to light, impaired blue/green color discrimination).

Seek medical attention right away if any of these severe side effects occur:

Severe allergic reactions (rash, hives, difficulty breathing, tightness in the chest, swelling of the mouth, face, lips, or tongue) , changes in heartbeat, chest pain, fainting, nausea, painful or prolonged erection (lasting more than four hours), severe dizziness, sudden decrease or loss of vision in one or both eyes, urinary tract infection.

This is not a complete list of all side effects that may occur. If you have questions or need medical advice about side effects of Viagra, contact your doctor or health care provider. You may report side effects to the FDA at 1-800-FDA-1088 (1-800-332-1088).

If an overdose is suspected:

Call 911 or get to an emergency room as soon as possible. Symptoms of an overdose may include fainting, prolonged erection and/or severe dizziness.