Viagra (sildenafil) is a phosphodiesterase (PDE) inhibitor specially intended for patients diagnosed with erectile dysfunction and unable to perform sexually as a result. Make sure you always take this drug as recommended. If you are using or are going to use any other drugs – it's a good idea to make a list and show to your doctor. You will need to report any other erectile dysfunction meds, HIV protease inhibitors, nevirapine, barbiturates, medications for high blood pressure, erythromycin, certain antifungals, beta blockers, rifabutin, anticoagulants, efavirenz, seizure medications, bosentan, rifampin, amlodipine, cimetidine, or alpha blockers, as well as street drugs that contain nitrates. Some interactions can make your treatment inefficient and even dangerous – so you must let your doctor know about all of them. There is no need to worry if you get headache, memory problems, warmth or redness in your face or chest, back pain, upset stomach, or stuffy nose, as those mild side effects will most probably disappear on their own. Make sure you tell your health care provider if the mild side effects mentioned change in intensity and start to interfere with your everyday life, as a dose adjustment may be needed.