A study carried out by scientists at Queens University of Belfast has suggested that men who take Viagra to pep up their sex lives could be impairing their fertility.
Scientists have carried out laboratory experiments which indicate that the anti-impotence drug can damage sperm. They warn that younger men trying for a family should think twice before using
Viagra recreationally.
The findings also raise questions for fertility clinics, many of which give the drug to both men and women.
Researchers found that sperm exposed to Viagra became more active. But at the same time a mechanism used by sperm to penetrate the egg wall during fertilisation was greatly speeded up.
Known as the "acrosome reaction", it involves firing an armour-piercing warhead of digestive enzymes at the egg.
The study showed that this was likely to happen to sperm exposed to Viagra .
Dr Sheena Lewis, director of the Reproductive Medicine Research Group at Queen's said: "The fact that this sperm function is impaired by the presence of Viagra is worrying."
The scientists, who present their findings today at the British Fertility Society's annual conference in Cheltenham, studied 45 samples of human semen.
Pfizer, the makers of Viagra , were contacted for a comment but did not offer one.