Viagra is a prescription medication used to treat erectile dysfunction (ED). Its generic name is sildenafil citrate, and it was the first oral ED treatment approved by the FDA, gaining approval in 1998. It works by increasing blood flow to the penis during sexual arousal, helping men achieve and maintain an erection.
How Viagra Works in the Body
An erection depends on blood flow. When you’re sexually aroused, nerve endings in the penis release a chemical signal called nitric oxide. This signal triggers a chain reaction that relaxes the smooth muscle in penile blood vessels, allowing them to widen and fill with blood.
A specific enzyme in the body normally breaks down the messenger molecule (called cGMP) that keeps those blood vessels relaxed. Viagra blocks that enzyme, so the messenger molecule sticks around longer and the blood vessels stay open. The key point: Viagra doesn’t create arousal on its own. It amplifies the body’s natural response to sexual stimulation. Without arousal, the drug has little effect on erections.
How Effective It Is
In large clinical trials involving nearly 1,800 patients with ED, the results were dose-dependent. At the lowest dose (25 mg), 63% of patients reported improved erections. That number rose to 74% at 50 mg and 82% at 100 mg. By comparison, only 24% of patients taking a placebo reported improvement. These trials lasted 12 to 24 weeks and included men whose ED had physical causes (58%), psychological causes (17%), or a mix of both (24%).
Dosage and Timing
The standard starting dose for most adults is 50 mg, taken about one hour before sexual activity. It can be taken anywhere from 30 minutes to 4 hours beforehand, giving a reasonable window of flexibility. For adults 65 and older, the typical starting dose is lower, at 25 mg. The maximum is one dose per day.
A high-fat meal can delay absorption by roughly an hour. The drug still works, but it takes longer to kick in. Taking it on an empty stomach or after a lighter meal produces faster results. Alcohol is a bigger concern: it can make erections harder to achieve on its own, which directly undercuts what Viagra is trying to do. Drinking also increases the likelihood of side effects like flushing, headaches, dizziness, and drops in blood pressure.
Common Side Effects
The most frequently reported side effects are headache, facial flushing, nasal congestion, indigestion, and temporary changes in vision (such as a blue-green tint or increased light sensitivity). These are generally mild and resolve on their own within a few hours. Dizziness can also occur, particularly in combination with alcohol.
Rare but serious side effects include a sudden decrease or loss of hearing, a sudden loss of vision in one or both eyes, and priapism (an erection lasting longer than four hours that doesn’t resolve). These require immediate medical attention.
Who Should Not Take It
The most critical safety concern involves nitrate medications, which are commonly prescribed for chest pain (angina). Taking Viagra alongside nitrates can cause a dangerous and potentially life-threatening drop in blood pressure. This interaction is not a matter of degree; the two should never be combined. The same applies to recreational drugs called “poppers,” which contain nitrates.
People with severe heart disease, very low blood pressure, or recent stroke or heart attack are also typically advised against using it. Because Viagra affects blood vessels throughout the body, not just in the penis, anyone taking blood pressure medications should discuss potential interactions with a prescriber before use.
Generic Availability
Generic versions of sildenafil have been available for several years and are significantly cheaper than the brand-name product. The FDA has approved generic sildenafil, and multiple manufacturers produce it. If you’re purchasing online, stick to verified pharmacies. Counterfeit versions sold through unregulated websites are a well-documented problem, and these products may contain incorrect doses, wrong ingredients, or no active ingredient at all.
Viagra’s Other Medical Use
The same active ingredient, sildenafil, is also used under a different brand name (Revatio) to treat pulmonary arterial hypertension, a condition where blood pressure in the arteries of the lungs is dangerously high. In this context, the drug relaxes blood vessels in the lungs rather than the penis, improving the heart’s ability to pump blood through them. The doses used for this condition are different from those used for ED, and the two brand names are not interchangeable.