The sex hormone progesterone, which is especially prevalent in the second
half of the menstrual cycle, has been shown to make female monkeys much more
vulnerable to SIV, the monkey version of HIV.
Two contraceptives, the implant Norplant, and Depo Provera, which is injected
Reports indicate that 14 out of 18 monkeys given the hormone became infected
with SIV, compared to just 1 of 10 monkeys that did not receive the hormone.
The findings are not necessarily applicable to humans, but experts say the
results support earlier theories linking hormone levels and susceptibility to
The National Institute of Child Health Development is also investigating
whether the issue of hormonal contraceptives increases HIV risk. The agency
recently reported that the physical effects of hormonal contraceptives may
affect HIV transmission
. "Women might be more susceptible during menses,
after menopause, or if they are on hormonal contraceptives." said Pamela
Stratton, an NICHD researcher.