Common antidepressant drugs may reduce some men's fertility by damaging the DNA in their sperm, according to scientists.

A study of 35 healthy men given paroxetine - sold as Paxil or Seroxat by GlaxoSmithKline - found that, on average, the proportion of sperm cells with fragmented DNA rose from 13.8 per cent before treatment to 30.3 per cent after just four weeks.

Similar levels of sperm DNA damage have been linked to problems with embryo viability in couples trying to have children. The research by Peter Schlegel and Cigdem Tanrikut of the Cornell Medical Center in New York was reported in New Scientist magazine and is due to be presented in November at a meeting of the American Society for Reproductive Medicine.

"The fertility potential of a substantial proportion of men on paroxetine may be adversely affected by these changes in sperm DNA integrity," the experts concluded.

The study adds to concerns voiced by the same doctors in 2006, after finding that two men had developed low counts of healthy sperm following treatment with two different selective serotonin-reuptake inhibitors (SSRIs).

SSRIs like Paxil/Seroxat and Eli Lilly's Prozac, both of which are now available generically, are the most commonly prescribed class of antidepressant.

Glaxo said it was reviewing the investigators' findings, since the study was not conducted by the company.

"These medicines remain an important option, in addition to counselling and lifestyle changes, for treatment of depression and this study should not be used to cause unnecessary concern for patients," a spokeswoman said.

"Patients should discuss their situation with their doctor before stopping use of their medicine."

Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield, said the apparent increase in sperm DNA damage was "alarming", although he noted the level at which damage becomes clinically significant was open to debate.

"It is a shame that the authors appear not to have conducted a randomised controlled trial which would be the most scientific way to investigate the drugs effects, but I agree that the results are of concern and need to be investigated further," he said.

SSRIs have long been known to depress libido in some men and previous research has also found that women taking the medicines are more likely to have a low birth weight baby.

A copy of the study abstract was made available to Reuters.

Reuters