Learn how long you should wait between Viagra doses to stay safe, avoid side effects, and get the best results from sildenafil. Viagra (sildenafil) is used to treat erectile dysfunction or impotence in men. Includes Viagra side effects, interactions and indications. So, how long does sildenafil last? And how long does it take for sildenafil to work? All PDE5 inhibitors—a class of erectile dysfunction drugs—last for varying durations, so timing them right is critical to avoid going soft during sex. Medicines like tadalafil last up to 36 hours, while vardenafil and sildenafil wear off after about four. Viagra (sildenafil), a medicine to treat erectile dysfunction (ED), can last for about four hours or more in some people. It should be taken 30 minutes to an hour before sexual activity. The effects of Viagra (sildenafil) are typically strongest about an hour after consumption, so it is best to take it an hour before sexual activity, though it can be taken up to 4 hours beforehand. How Long Does Viagra Last? By continually increasing blood flow to the privates, Viagra gives you a window of several hours (up to four) in which you can get hard with addition of stimulation. Viagra (sildenafil) is a brand-name prescription drug that’s used to treat erectile dysfunction (ED). Learn about side effects, warnings, dosage, and more. But your diet, your overall health, the medications you’re taking, underlying conditions, and much more can all affect the amount of time Viagra takes to work in your body and how long it lasts. Don't take Viagra if you take nitrates. Nitroglycerin and other long-acting nitrates used to treat chest pain are contraindicated with Viagra, which can cause the blood pressure to drop to dangerously low levels and lead to a heart attack or stroke. It continues to decrease over the next 20 hours. Viagra may take longer to work if you take it after a fatty meal because fat slows down absorption in your stomach. Men over age 65 and men with liver disease or severe kidney disease may have longer effects from Viagra, and the dose may need to be lower.