· For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed.Using alcohol or tobacco with certain medicines may also cause interactions to occur. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. Sildenafil may cause side effects. You may take this medicine with or without food. This includes prescription or nonprescription over-the-counter [OTC] medicines and herbal or vitamin supplements.RESOURCES GETTING STARTED WITH VIAGRA Your doctor has determined that VIAGRA may be right for you. Follow his or her instructions carefully to help you get the best results from treatment. VIAGRA is available by prescription only in 25 mg, 50 mg, and mg tablets. Not actual size. TIPS FOR TAKING VIAGRA.  · For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed. Take sildenafil as needed before sexual activity. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. Sildenafil usually should not be .Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine. Sildenafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. If you are taking sildenafil to treat erectile dysfunction, you should know that it does not cure erectile dysfunction or increase sexual desire. It is important to tell your doctor about any heart problems you have now or may have had in the past. If too much is used, the chance of side effects is increased. Brand names Why is this medication prescribed?