Make sure you tell your doctor if you have any other medical problems, especially: Abnormal penis, including a curved penis or birth defects of the penis—Chance of problems occurring may be increased and this medicine should be used with caution in these patients. Although not all of these side effects may occur, if they do occur they may need medical attention. Population pharmacokinetic data from patients in clinical trials also indicated a reduction in sildenafil clearance when it was co-administered with CYP3A4 inhibitors such as ketoconazole, erythromycin, or cimetidine [see Dosage and Administration 2. It is eliminated predominantly by hepatic metabolism mainly CYP3A4 and is converted to an active metabolite with properties similar to the parent, sildenafil. Sexual function data were also recorded by patients in a daily diary. Side Effects Along with its needed effects, a medicine may cause some unwanted effects. If you need emergency medical care for a heart problem, it is important that your doctor knows when you last took sildenafil. · How GoodRx Works. Compare prices. Drug prices vary by pharmacy. Use GoodRx to find current prices and discounts. Get free coupons. GoodRx coupons can help you pay less than the cash price for your prescription. Show to your pharmacist. It’s easy. Just bring your free coupon to the pharmacy when picking up your prescription. Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult . Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision.