Antidepressants taken by millions of men
could be impairing their fertility by causing damage to the
DNA in their sperm.
In 2006, Peter Schlegel and Cigdem Tanrikut of the Cornell
Medical Center in New York City reported that two men had
developed low counts of healthy sperm after taking two different
selective serotonin-reuptake inhibitors (SSRIs), the most
commonly prescribed class of antidepressant.
Now Schlegel's team has given 35 healthy men doses of a third
SSRI called paroxetine, sold as Seroxat or Paxil, over five
weeks, and examined their sperm before treatment and four
Superficially, the men's sperm seemed healthy - amounts of
sperm and semen, and the shape and motility of sperm, were
all normal. But when the team looked at DNA fragmentation
in the sperm, using the TUNEL method, a worrying picture emerged.
On average, the
proportion of sperm cells with fragmented DNA rose from 13.8
per cent before taking paroxetine to 30.3 per cent after just
Similar levels of sperm DNA damage have been linked to problems
with embryo viability. For example, in couples undergoing
IVF, studies have found that where the man has more sperm
with damaged DNA, fewer embryos form and those that do are
less likely to implant successfully into the woman's uterus.
As a result, fertility specialists regard a fraction of 30
per cent of sperm with DNA damage as being "clinically significant",
says Douglas Carrell, a specialist in male infertility at
the University of Utah in Salt Lake City.
Schlegel's team is concerned that some men currently taking
SSRIs may be suffering damage to their fertility. The team
will present its results in November at a meeting of the American
Society for Reproductive Medicine in San Francisco, California.
Janet Morgan, a spokeswoman for GlaxoSmithKline, which sells
paroxetine, says: "This study was not conducted by GSK, and
therefore we are currently reviewing the investigators' findings.
We take seriously our responsibility to ensure our medicines
are used safely."
Schlegel's results have come as no great surprise to some
researchers, however. "I think a lot of us around the world
have had data that have pointed in this direction and have
been suspicious," says Carrell.
He says that Schlegel's work is a "good preliminary study"
but adds that studies of the longer term effects of SSRIs
on sperm are also necessary.
SSRIs are known to slow the movement of sperm through the
male reproductive system, an effect that has been exploited
to help treat premature ejaculation. Schlegel believes that
this extra time spent travelling from the testes causes sperm
to accumulate DNA damage.