The most common side effects of sildenafil include headaches, nausea, and skin flush, but please ask your doctor for a complete list. Also, be sure to tell your physician immediately if you experience an erection that lasts longer than four hours, alterations in your vision, or any other significant changes. Sildenafil should not be taken in conjunction with medications that contain nitrates and should be used cautiously in people with low blood pressure. Ask your doctor for a full list of medications and conditions that should not be combined with sildenafil. Over fifty percent of men over the age of forty suffer from some sort of erectile dysfunction, and Viagra can be quite effective at easing symptoms. However, this drug should always be used under the direct care of a physician. Please ask for and review all of the information provided by your doctor before taking sildenafil.