New research in mice suggests that women who use the injectable contraceptive Depo-Provera may have a higher risk of infection with genital herpes than non-users.

Study author Dr. Charu Kaushic and colleagues of McMaster University in Canada injected mice with Depo-Provera or left them contraceptive-free, and then exposed them to herpes simplex virus type-2. Normally, mice will develop genital herpes only when exposed to very high concentrations of the virus. But the researchers discovered that mice given Depo-Provera became infected with only one-hundredth the virus concentration needed to infect mice not given the contraceptive. Furthermore, examinations of antibodies showed that mice injected with Depo-Provera had one-tenth as many antibodies directed against the virus as mice that had not received the contraceptive. The full report, "Progesterone Increases Susceptibility and Decreases Immune Responses to Genital Herpes Infection," was published in the Journal of Virology (2003;77:4558-4565).

If a similar pattern occurs in women, these findings suggest that women who use Depo-Provera might be particularly susceptible to developing genital herpes when exposed to the virus, Kaushic said. Julie Lux, spokesperson for Depo-Provera's manufacturer, Pfizer, said, "For more than 30 years, Depo-Provera has been used safely and effectively by women around the world." Lux also pointed out that the product packaging clearly indicates that Depo-Provera offers no protection against STDs, so anyone looking to prevent disease as well as pregnancy needs to use a condom, too.

Kaushic noted that the new findings add to past research suggesting that Depo-Provera can increase the risk of other STDs, including chlamydia. "Do I think Depo-Provera might have an effect on susceptibility to herpes and STDs in women? Quite likely, based on these studies" and others, Kaushic said.

Users of the contraceptive who are not in a stable relationship and have other risk factors for genital herpes, such as multiple sexual partners, "might want to take extra precautions to make sure that if their susceptibility is increased, they are protecting themselves," Kaushic said. Depo-Provera is injected every three months in the arm or buttocks to prevent pregnancy.

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