The amount of Viagra you take affects how long it stays in your system. The smallest available dose, 25 milligrams (mg), won’t last as long as the largest available dose, 100 mg. Viagra (sildenafil) is a prescription medication that treats erectile dysfunction (ED). It works by relaxing smooth muscles and arteries in your penis to help you achieve and maintain an erection. Viagra’s effects typically last for at least 4 hours. But it can stay in your system for up to 20 hours (close to a day). Avoid taking Viagra at the same time as nitrates such as nitroglycerin. Viagra lasts for about four hours, but it can last longer in some people. Viagra should be taken 30 minutes to an hour before sexual activity. Older age or certain drugs can make Viagra stay in your system longer. Viagra inhibits the breakdown of cGMP, which makes an erection harder and longer lasting. Since this process only starts with stimulation of the penis and the release of nitric oxide, Viagra will not give you an erection without your penis also being stimulated. Viagra can make your penis stay erect longer, but it may not make you last longer. Medicine › Drugs How Long Does Viagra Stay in Your System: Half-Life & Effects Viagra stays active for 4–6 hours, but traces linger longer. Learn how age, liver health, and food affect how your body processes sildenafil. Viagra’s effects typically last 4–6 hours, but the drug stays in your system longer. Here’s what affects how quickly your body clears it. Viagra typically works for 4–6 hours, but several factors affect how long it stays in your body. Here’s what actually influences its timing and duration. Learn how long Viagra stays in your system, its half-life, and what factors affect its duration. Understand the medication's effects and interactions for safe use. Learn how long sildenafil (Viagra) stays in your system, including half-life, duration of effects, and factors that affect how quickly it wears off. Sildenafil (Viagra) stays in your system for up to 24 hours, with its strongest effects lasting about four hours after use.