Viagra 'could harm fertility'

Taking Viagra could damage a man's chances of becoming a father, according to a study.

The drug is designed to increase the flow of blood to the penis to overcome impotence, but it is also used recreationally.

However, it speeds up chemical changes within sperm making them infertile by the time they reach an egg, researchers found in laboratory tests.

The findings raise questions for fertility clinics, where the drug may be used in obtaining sperm for treatment.

Scientists from Queen's University, Belfast will present the research today at the British Fertility Society's annual conference in Cheltenham.

A spokesman for Pfizer, manufacturer of Viagra, said there has been no clinical evidence of the drug affecting fertility.