Some medications should not be taken with sildenafil. You are encouraged to report adverse events related to Viatris products by calling U. This medicine works best when you take it on an empty stomach an hour before sex. Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. When hypertension occurs in the lungs, the heart must work harder to pump enough blood through the lungs.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 . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or . Why is this medication prescribed? Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men.