Viagra also called sildenafil is a medicine that is commonly used to treat erectile dysfunction in men. It works to increase the blood flow of the body for an erection in the body. You must read the directions and causes on the packet before use. Do not take an overdose as it can affect the body. If you are experiencing any side effects from this, you must ask a doctor and stop taking the medicine immediately. One thing that you must keep in mind is to avoid having grapefruit juice or any product that contains grapefruit extract with Viagra it can give you a side effect.