Stop taking VIAGRA and call your healthcare provider right away if you have any sudden vision loss sudden hearing decrease or hearing loss. There were some reports of headaches and nausea, however. This medicine works best when you take it on an empty stomach an hour before sex. 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. You can take it in a small dose daily or in a larger dose as needed. The products discussed in this site may have different product labeling in different countries. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction.Other options. There are several options to treat erectile dysfunction aside from oral medications like Cialis, including: erectile dysfunction pump, which can be a penis or . There’s a New Over-the-Counter ED Drug. Should You Be Taking It? Doctors say it could be a “game-changer.” By Erica Sweeney Published: Save Article Image . Viagra is usually taken only when needed, 30 minutes to 1 hour before sexual activity. You may take it up to 4 hours before sexual activity. Other drugs may interact with .