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Ever since Viagra worked
for men - and didn't for women - researchers have been searching
for a drug that turns women on. Now a hormone-like drug may hit
the spot, by targeting not the genitals, but the brain.
The way
Viagra works is simple; it dilates blood vessels, increasing
blood flow in the genitals. This purely physical
effect seems to be sufficient for most men to perform and enjoy
sex.
But women are more complicated. "The difference between
male and female orgasms is that brain effects are more important
in women," says John Stevenson, an endocrinologist at
the Royal Brompton and Harefield NHS Trust. In other words,
physical arousal doesn't happen without desire. And that can
be much harder to trigger.
" People may get the sensory
input, but they don't think, 'ooh I'm horny'."
According
to James Pfaus, a behavioural neurobiologist at Concordia University
in Montreal, Canada, disorders of sexual
desire affect 30% of women in North America and Europe. The
loss of sex drive may be down to personal factors in many cases,
but Pfaus says that the cause is sometimes physiological.
" People may get the sensory input, but they don't think,
'ooh I'm horny'," he says.
All in the brain
Pfaus believes that a drug called PT-141 could help
women in this situation by stimulating their brains to increase
libido. PT-141 mimics a hormone called alpha-melanocyte-stimulating
hormone, which binds to certain receptors in the brain and
is thought to stimulate sexual activity. The drug has already
been shown to work on men who don't respond to Viagra.
To
test whether females respond to it too, Pfaus and his
team administered the drug to groups of 20 or 40 rats. The
animals each received one of four doses of PT-141, and then
each group was tested for a different sign of sexual desire,
including showing interest in individual males and changing
body position to aid sexual intercourse.
In all the groups,
the higher the dose of PT-141, the more sexual behaviour
the females displayed. The next step, says
Pfaus, is to test the drug in women.
Stevenson agrees the
approach looks promising. But he points out that women who
lose their sex drive are often in menopause
and suffer from other symptoms too, such as hot flushes and
mood swings. The drug could be most useful in combination
with other therapies, he suggests. |
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