May make this condition worse. Kidney disease that needs to be treated with dialysis. If you experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. Ask your doctor if you have any questions. When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side effects. · Viagra is used as needed, meaning you only take a dose prior to sexual activity. Viagra is a prescription drug used to treat erectile dysfunction. Learn how to lower long-term costs, and more. Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is mg. Don’t take sildenafil (Viagra) more than once daily (at any dose). Written by Brian Leonard, PharmD, BCACP, BCGP. 1. Avoid taking Viagra with a large meal or high-fat meal. Viagra blood levels peak an hour after you swallow the tablet on an empty stomach. According to Ramin, if you eat a large or high-fat.