01 April 2004
ByAppeared in BioNews 252
Viagra, the 'wonder-drug' promoted for its ability to relieve impotence in men, may have some unwanted side-effects. Research presented today in Cheltenham, UK, at the annual meeting of the British Fertility Society, suggests that men who are taking Viagra when trying to start a family may actually be decreasing their ability to father a child. However, Viagra manufacturers Pfizer deny that the drug causes fertility problems.
Viagra was designed to enable an increase of blood flow to the penis to overcome impotence problems. However, since its release it has increasingly been used 'recreationally', and is also used by fertility clinics in order to aid patients' semen production. Viagra is what is known as a 'phosphodiesterase inhibitor', a type of chemical known to affect sperm function, so the study looked at what effect the drug has on sperm. The researchers discovered that using Viagra speeds up chemical changes within sperm, rendering them infertile by the time they reach an egg. This chemical change, known as the acrosome reaction, normally only occurs when a sperm reaches an egg, and is when sperm release enzymes that break down the outer layer of the egg allowing the sperm head to penetrate it more easily. However, if the acrosome reaction occurs too early, the sperm become ineffective and unable to enter the egg, as they have no digestive enzymes left.
Scientists from the School of Medicine, Obstetrics and Gynaecology at Queen's University, Belfast, took 45 semen samples and split them into two groups. Half of the samples were treated with Viagra, while the other half was used as control. The research team found that while Viagra increased sperm motility, up to 79 per cent more sperm in the Viagra-treated samples had clearly undergone premature acrosome reactions. These findings lead the researchers to say they had 'significant concerns for Viagra use in assisted reproduction'. They added that the findings echo previous studies in mice that showed that the presence of Viagra meant that fewer eggs would be fertilised and fewer resulting embryos developed normally.
Dr Sheena Lewis, a member of the team, said that their 'message is that caution should be taken when using recreational drugs if you are hoping to start a family'. But a representative of the European Society for Sexual Medicine, Dr John Dean, said it was important that the study wasn't reported in an alarmist fashion, adding that sperm is highly sensitive in laboratory conditions. 'Childless couples - and the general population - should be aware that in the five years that Viagra has been around no overall detrimental effect on fertility has been observed', he said.
However, Pfizer says that there has been no evidence of Viagra affecting fertility following its use by 23 million men over six years. 'It's one study and it was in a test tube basically, not in real people', said spokesman David Watts.