ED can sometimes signal an underlying medical problem, like heart disease or diabetes , that needs to be treated separately. Medicines that you take by mouth are called oral medicines. 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. Vardenafil usually works for 4 to 5 hours. It might be a while before MED is available at your local pharmacy. Side effects Side effects of oral ED medicines are often mild. Avanafil Stendra.Eroxon, the brand name for MED, is currently available in Belgium and the U.K. It claims to “help you get an erection within 10 minutes.” About half of all men will . In most males,* Viagra works within 1 hour after it’s taken. It’s possible that Viagra can begin working within 30 minutes of being taken. But other times, it may take up to 4 . Can I buy generic Viagra over the counter or do I need a prescription? In the U.S. and most other countries, generic Viagra is only available with a prescription.