Do not use the medication if you take medicines called “nitrates”, use street drugs called “poppers” such as amyl nitrate and butyl nitrate, are allergic to avanafil or any of the ingredients in Stendra. Do not drink too much alcohol when taking Stendra. Drinking too much alcohol when taking Stendra can increase your chances of getting a headache or getting dizzy, increasing your heart rate, or lowering your blood pressure. Do not take Stendra if you take any medicines called “nitrates.” Nitrates are used to treat chest pain (angina). A sudden drop in blood pressure can cause you to feel dizzy, faint, or have a heart attack or stroke. Stendra can interact with medications such as nitrates, HIV protease inhibitors, like ritonavir, oral antifungal medicines, like ketoconazole, antibiotics, such as clarithromycin, alpha blockers such as terazosin, doxazosin, prazosin medicines that treat high blood pressure, other medicines or treatments for erectile dysfunction. Before using Stendra have or have had heart problems such as a heart attack, irregular heartbeat, angina, or heart failure, have had heart surgery within the last 6 months, have had a stroke, have low blood pressure, or high blood pressure that is not controlled, have a deformed penis shape, have had an erection that lasted for more than 4 hours, have problems with your blood cells such as sickle cell anemia, multiple myeloma, or leukemia, have retinitis pigmentosa, a rare genetic (runs in families) eye disease, have ever had severe vision loss, including an eye problem called non-arteritic anterior ischemic optic neuropathy (NAION), have bleeding problems, have or have had stomach ulcers, have liver problems, have kidney problems or are having kidney dialysis.