A priapism is a persistent erection of the penis that lasts for four hours or often much longer. Although many men may think this might be a good and desirable thing to have, there are a number of reasons why it isn't.

First, it may be a real nuisance since priapism can occur when a man doesn't have any sexual desire. Second, priapism can damage the erectile tissues of the penis permanently. And third, it can be extremely painful.

Priapism occurs because the blood that fills the spongy tissue in the penis to form an erection can't escape. This might be because of prolonged sexual intercourse, medical conditions such as polycythaemia or sickle-cell disease, or drug side effects. Very occasionally drugs used to treat impotence can cause priapism too.

The problem of priapism can be relieved immediately by releasing the blood from the penis. A doctor will do this at the local casualty (accident and emergency) department with a needle and syringe. But if the priapism persists or repeatedly occurs other treatments, such as injections into the penis of medicines known as sympathomimetics (which stimulate the nerves controlling the blood vessels) or surgery to shunt the blood out of the penis, may be needed.

If priapism is a side effect of medication then a more suitable medication can be prescribed. If it's because of an underlying medical condition then this can usually be treated.

This article was last medically reviewed by Dr Trisha Macnair in June 2008