The prescription medication Viagra, containing the active ingredient sildenafil citrate, was approved by the U.S. Food and Drug Administration in 1998 for the treatment of erectile dysfunction. In clinical trials, the most commonly reported side effects of Viagra were headache and flushing of the face, but these conditions were generally mild and short-lived. Although rare, serious side effects can occur while using Viagra, and a doctor should be consulted if these effects occur or persist.
Prolonged Erection
Rare side effects of Viagra include a prolonged erection lasting more than four hours, or priapism, a painful erection persisting for six hours or more. In these cases, blood is trapped in the penis and deprived of oxygen, which could lead to tissue damage.
Immediate medical attention should be sought in cases of prolonged erection to prevent permanent injury. The erection may subside on its own, or the doctor may choose to treat it with medication or aspiration, in which blood is drained from the penis with a small needle, alleviating the pain and the erection.
Vision Changes
In clinical trials, 3 percent of patients reported mild vision changes, including blurred vision, increased light sensitivity and difficulty distinguishing the colors blue and green. These vision changes were more common among patients taking the 100 mg dose of Viagra, according to Pfizer.
Infrequently, Viagra users may experience sudden vision loss in one or both eyes. This can be a sign of a condition called non-arteric ischemic optic neuropathy, or NAION, in which the flow of blood to the optic nerve is blocked. It is unknown if this condition is caused by Viagra, the patient's health conditions or a combination of factors, states the U.S. Food and Drug Administration. If any vision changes occur, you should stop taking Viagra and contact your doctor.
Interactions
You should discuss any medications you're taking with your doctor before using Viagra. Viagra is particularly dangerous if you're taking nitrates, which may be prescribed for chest pain or heart conditions. Nitrate is also present in some recreational drugs. The combination of Viagra and nitrate can result in a life-threatening drop in blood pressure. You should also avoid Viagra if you're taking other medications that include sildenafil or PDE5 inhibitors.
Overdose
Viagra is prescribed in 25, 50 and 100 mg doses, and doctors may start with the lowest dose for men over age 65 or people who use certain medications or have some underlying health conditions. If Viagra isn't having the desired effect, speak to your physician; don't exceed the dosage or take Viagra more than once per day. Exceeding your prescribed dosage of Viagra can increase the frequency, duration or severity of the side effects you experience.
References
- Drugs@FDA: Viagra Label and Approval History
- Pfizer: Viagra Prescribing Information (PDF)
- MayoClinic.com: Priapism
- U.S. Food and Drug Administration: FDA Updates Labeling for Viagra, Cialis and Levitra for Rare Post-Marketing Reports of Eye Problems
- Texas Heart Insititute Heart Information Center: Nitrates
