Other uses for this medicine This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information. The following information includes only the average doses of this medicine. Take sildenafil exactly as directed. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. 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. You can take it in a small dose daily or in a larger dose as needed.FAQs What to consider Cost Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. . Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 . For treatment of erectile dysfunction: 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 .