Sildenafil is a medication approved to treat two conditions: erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). Most people know it by the brand name Viagra, which is the ED version. The same drug is also sold under the brand name Revatio for pulmonary arterial hypertension. Though the active ingredient is identical, the doses and treatment goals are quite different.
Treating Erectile Dysfunction
Sildenafil’s most well-known use is helping men achieve and maintain erections. It works by relaxing blood vessels in the penis, which increases blood flow when a person is sexually aroused. It does not cause an erection on its own. Sexual stimulation is still required for the medication to work.
The standard starting dose for ED is 50 mg, taken about an hour before sexual activity. Depending on how well it works and how you tolerate it, the dose can be adjusted down to 25 mg or up to a maximum of 100 mg. It should not be taken more than once per day.
Effects can begin in as little as 30 minutes and last for up to 4 hours. The drug and its active byproduct both have a half-life of about 4 hours, meaning the body clears them relatively quickly compared to some other ED medications. In clinical trials involving men with spinal cord injuries, 75% of those taking sildenafil reported improved erections after 28 days, compared to just 7% on placebo.
Treating Pulmonary Arterial Hypertension
Pulmonary arterial hypertension is a condition where blood pressure in the arteries of the lungs becomes dangerously high, forcing the heart to work harder to pump blood through them. Left untreated, it can lead to heart failure. Sildenafil helps by relaxing the blood vessel walls in the lungs, lowering that pressure and easing the workload on the heart.
For PAH, the dosing looks completely different from the ED version. Instead of a single large dose taken as needed, the PAH regimen calls for 20 mg taken three times a day, spaced 4 to 6 hours apart. This keeps a steady level of the drug in the bloodstream throughout the day. Doses higher than 20 mg three times daily are not recommended for this condition.
Off-Label Uses
Because sildenafil improves blood flow by relaxing blood vessels, doctors sometimes prescribe it for conditions beyond its two approved uses. One example is Raynaud’s phenomenon, a condition where blood vessels in the fingers and toes constrict excessively in response to cold or stress, sometimes leading to painful sores called digital ulcers. This is especially common in people with systemic sclerosis, an autoimmune disease that damages blood vessels and surrounding tissue. A European clinical trial tested higher doses of sildenafil in 57 people with Raynaud’s secondary to systemic sclerosis, though no sildenafil product is officially licensed for this purpose.
Sildenafil has also been studied for high-altitude pulmonary edema, where fluid builds up in the lungs at extreme elevations. These off-label uses share the same underlying logic: the drug opens up constricted blood vessels wherever they’re causing problems.
How Food Affects Absorption
Sildenafil can be taken with or without food, but eating a high-fat meal before taking it changes the timing. A fatty meal delays the drug’s peak concentration by roughly 60 minutes and reduces that peak by about 29%. The total amount your body absorbs over time stays about the same, so the drug still works. It just kicks in later than expected. If timing matters, taking sildenafil on an empty stomach or after a light meal gives the most predictable results.
Important Safety Considerations
The most critical safety concern with sildenafil is its interaction with nitrate medications, which are commonly prescribed for chest pain (angina). Both sildenafil and nitrates lower blood pressure by relaxing blood vessels. Taken together, they can cause a sudden, dangerous drop in blood pressure. This combination is strictly contraindicated, meaning it should never be used. If you take any form of nitrate, whether as a pill, patch, or spray, sildenafil is not safe for you.
Common side effects tend to be mild and related to the same blood vessel relaxation that makes the drug work: headaches, facial flushing, nasal congestion, and sometimes temporary changes in color vision, such as a bluish tint. These effects generally resolve within a few hours as the drug leaves the body.