Viagra is a prescription medication used to treat erectile dysfunction (ED). It works by increasing blood flow to the penis, helping men achieve and maintain an erection during sexual activity. First approved by the FDA in 1998, it was originally developed as a heart medication before researchers discovered its effects on erections during clinical trials.
How Viagra Works in the Body
An erection depends on blood flowing into the penis and staying there. When a man is sexually aroused, the body releases a chemical messenger called cyclic GMP, which relaxes the smooth muscle in blood vessel walls and allows them to widen. Normally, an enzyme called PDE5 breaks down this messenger, eventually ending the erection.
Viagra (sildenafil) blocks PDE5 from doing its job. With that enzyme out of the way, cyclic GMP builds up, the blood vessels stay relaxed longer, and blood flow to the penis increases. This doesn’t create an automatic erection on its own. Sexual arousal is still required to start the process. Viagra simply makes the body’s natural response work more effectively.
How Well It Works for ED
In clinical trials submitted to the FDA, 74% of patients taking the standard 50 mg dose reported improved erections, compared to 24% on a placebo. At the highest dose (100 mg), that number rose to 82%. In a long-term study, 88% of patients said the medication improved their erections over time.
Viagra also works for ED caused by specific medical conditions, though effectiveness varies. Among men with diabetes, 57% reported improvement versus 10% on placebo. For men with spinal cord injuries, 83% saw better erections. After radical prostatectomy (surgical removal of the prostate), the success rate was lower at 43%, likely due to nerve damage from the procedure. Men whose ED had a psychological cause responded best, with 84% reporting improvement.
Timing, Dosing, and Duration
The standard starting dose is 50 mg, taken about one hour before sexual activity. It can be taken anywhere from 30 minutes to 4 hours beforehand. The effect peaks around the 2-hour mark and gradually diminishes after that, though it can last up to 4 hours. The maximum frequency is once per day, and the dose can be adjusted down to 25 mg or up to 100 mg depending on how well it works and how you tolerate it.
Eating a heavy, high-fat meal before taking Viagra can slow absorption and delay when it kicks in. Grapefruit and grapefruit juice raise the drug’s levels in your body, which increases the chance of side effects. Alcohol doesn’t directly interact with the medication, but drinking heavily can worsen side effects like flushing, nausea, and dizziness, and make it harder to tell whether the drug is actually working.
Common Side Effects
The most frequently reported side effects are headache, facial flushing, nasal congestion, and indigestion. Some people notice temporary changes in vision, such as a bluish tint or increased light sensitivity, because a related enzyme in the eye is mildly affected. These side effects are generally mild and short-lived. They tend to be more noticeable at higher doses.
The Nitrate Interaction You Need to Know About
The most serious safety concern with Viagra is its interaction with nitrate medications, commonly prescribed for chest pain (angina). Nitrates include nitroglycerin patches, nitroglycerin tablets placed under the tongue, and isosorbide. Both nitrates and Viagra relax blood vessels. Taken together, they can cause a sudden, severe drop in blood pressure that reduces blood flow to the heart, potentially with fatal consequences. This combination is strictly contraindicated, meaning you should never take them together.
Because Viagra relaxes smooth muscle throughout the body, not just in the penis, it also has mild blood-pressure-lowering effects on its own. This is usually insignificant for most people but becomes dangerous when combined with drugs that do the same thing.
Viagra’s Other Medical Use
The same active ingredient, sildenafil, is sold under the brand name Revatio for a completely different condition: pulmonary arterial hypertension (PAH). In PAH, the blood vessels in the lungs become abnormally narrow, forcing the heart to work much harder to pump blood through them. Sildenafil relaxes those lung blood vessels in the same way it relaxes blood vessels elsewhere, lowering the pressure and improving the ability to exercise.
The dosing for PAH is very different from erectile dysfunction. Instead of a single dose taken as needed, PAH patients take 20 mg three times daily on an ongoing basis. This use is approved for both adults and children ages 1 to 17.
Off-Label Uses
Because sildenafil improves blood flow by relaxing blood vessels, doctors sometimes prescribe it for conditions beyond its two FDA-approved uses. One notable example is Raynaud’s phenomenon, a condition where blood vessels in the fingers and toes spasm in response to cold or stress, cutting off circulation and causing pain. In a controlled study of patients whose Raynaud’s wasn’t responding to other treatments, sildenafil reduced the frequency of attacks by about a third, cut the total duration of attacks nearly in half, and quadrupled blood flow velocity in the tiny capillaries of the fingers. In all six patients who had chronic digital ulcers (open sores on the fingertips from poor circulation), the wounds began healing visibly during treatment.
Brand Name vs. Generic Cost
Viagra’s patent expired and generic sildenafil became widely available starting in late 2017. The price difference is dramatic. Generic sildenafil has dropped to as little as 44 cents per 50 mg dose when purchased in quantities of 30, while brand-name Viagra costs over $67 per pill at list price. That works out to roughly $13 for a month’s supply of generic versus over $2,000 for the same amount of brand-name Viagra. The two are chemically identical. The generic simply lacks the brand name and the blue diamond shape.
Prices vary by pharmacy, so shopping around or using a discount coupon can make a significant difference. In one regional comparison, the cheapest price for six generic 100 mg tablets was under $10 at a supermarket pharmacy, while the same quantity of brand-name Viagra cost over $400 at every outlet checked.