In some patients, the use of VIAGRA with alpha-blockers can lead to a drop in blood pressure or to fainting medicines called HIV protease inhibitors, such as ritonavir Norvir , indinavir sulfate Crixivan , saquinavir Fortovase or Invirase , or atazanavir sulfate Reyataz some types of oral antifungal medicines, such as ketoconazole Nizoral and itraconazole Sporanox some types of antibiotics, such as clarithromycin Biaxin , telithromycin Ketek , or erythromycin other medicines that treat high blood pressure other medicines or treatments for ED VIAGRA contains sildenafil, which is the same medicine found in another drug called REVATIO. The body takes longer to absorb it after a high-fat meal or alcohol. You can take this medicine with or without food 30 minutes before sex, depending on the dose. Avanafil Stendra. It works for up to 36 hours. Many people have no side effects or only mild ones. You are encouraged to report adverse events related to Viatris products by calling U.Used for Erectile Dysfunction. Sildenafil (Viagra) is taken by mouth to treat erectile dysfunction (ED). You take it only as needed, typically about an hour before sexual activity (but you can take it anywhere between 30 minutes to 4 hours before sex). Don’t take sildenafil (Viagra) more than once a day because doing so can put you at higher. The recommended dosage of Viagra for erectile dysfunction (ED) is 50 mg, taken as needed about 1 hour before sexual activity. You can take it 30 minutes to 4 hours before sexual activity. And you.  · You’ll likely start with a Viagra dose of 50 mg. You’ll typically take Viagra about 1 hour before sex. You can take the drug 30 minutes to 4 hours before you anticipate sexual activity.