A study found that a hormone commonly used in hormone replacement therapy and as a form of contraceptive could increase levels of aggression and anxiety and decrease libidos in women who take the hormone.

Researchers believe the hormone, medroxyprogesterone (MPA), could explain the symptoms of mood swings, depression and loss of sex drive described by some of the women who took the MPA for contraception purposes and hormone replacement therapy.

In a study, three separate hormone treatments were used to evaluate any behavioral changes in six female monkeys.

The three treatments were estrogen only, estrogen with natural progesterone and estrogen with MPA. The researchers focused on changes in aggression, anxiety and sexual behavior.

Results of the Study

• The monkeys treated with estrogen plus MPA exhibited distinctly higher levels of aggression and restless behaviors compared to the monkeys who received estrogen alone or estrogen with progesterone.

• There appeared to be a significant decrease in sexual behaviors among the monkeys who were treated with the MPA plus estrogen combination.

From these findings, researchers concluded that MPA with estrogen might produce a greater affect on the brain’s stress system than the treatment of natural progesterone.

In order to study the behavioral changes over an extended period of time, researchers have conducted studies involving observing aggression, anxiety and sexual behavior changes in monkeys over the course of 21 days, which is comparable to the monthly cycle for women taking contraceptives.

Journal of Clinical Endocrinology and Metabolism June 2004;89(6):2963-72