The most common reported side effects of Sildenafil include, but are not limited to, lowered blood pressure, dizziness, back pain, headache, muscle aches, stomach discomfort following meals, blurred vision, flushing, stuffy or running nose, trouble sleeping and diarrhea. If these side effects become persistent and/or bothersome, please contact your provider to discuss whether or not the medication should be stopped. If you start to experience rare, but serious, side effects such as a prolonged painful erection for longer than 4 hours (priapism), sudden loss of vision, double vision, hearing problems, convulsions, trouble breathing or hives- please seek medical attention immediately.