Medicines that you take by mouth are called oral medicines. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. Erectile dysfunction can be caused by a variety of factors , including age, cardiovascular problems, diabetes, and other conditions that affect nerve function or blood flow. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox. It depends on the platform and insurance provider. When a man is sexually stimulated, his body’s normal response is to increase blood flow to his penis to produce an erection. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine.VIAGRA can cause your blood pressure to drop suddenly to an unsafe level if taken with certain other medicines. Do not take VIAGRA if you take any other 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. In addition to Viagra, REX MD also offers brand-name Cialis and generic Cialis (tadalafil). Both Viagra and sildenafil are available in mg, mg, and mg doses. The average length of time Viagra lasts. On average, Viagra lasts between 2 and 3 hours before its effects start to diminish. Viagra can last up to 5 hours or longer depending on your dosage, your.