ATLANTA, June 7 (UPI) -- A U.S. study finds a synthetic hormone used in birth control and hormone replacement therapy makes monkeys more aggressive.
Medroxyprogesterone acetate, a synthetic form of the naturally occurring hormone progesterone, increases aggression and anxiety and reduces sexual activity in female monkeys, reported researchers at Emory University and the Center for Behavioral Neuroscience in Atlanta.
The researchers said the findings may explain anecdotal reports of mood and libido changes in women using birth control and HRT.
Scientists compared the behavior of six female pigtail macaques that each had received one week's treatment with estrogen, estrogen plus natural progesterone or estrogen plus MPA. Monkeys receiving MPA were significantly more aggressive and anxious, and had markedly reduced sexual activity.
Researcher Karen Pazol said unlike natural progesterone, MPA cannot be converted to the mood-regulating chemical allopregnanolone.
Pazol also is studying MPA's effects on monkeys over 21 days, the menstrual standard cycle for women taking birth control pills.
