If you are a young man who wants to have children you might want to think twice before taking Viagra. New evidence suggests that the drug could impair your fertility.

According to researchers from Queen's University in Belfast, Northern Ireland, UK, viagra has an effect on the sperm's ability to penetrate the wall of the egg. It reduces the sperm's ability to break through the membrane.

The researchers said that Viagra does make the sperm more active. However, it also causes the sperm to release digestive enzymes which pierce the egg wall to fertilise it before it has reached the egg. When it does reach the egg it cannot pierce the wall.

The researchers presented their finding at the British Fertility Society's annual conference, Cheltenham, UK.

They carried out laboratory tests. These tests indicated that Viagra could damage sperm.

They said that younger men who want to have children should be aware of this.