Women who use the injected contraceptive Depo-Provera have a higher rate of sexually transmitted diseases, U.S. researchers reported on Monday.
This holds true even when behavior and other factors are taken into account, the research team at the National Institutes of Health, University of North Carolina and Johns Hopkins University in Baltimore found.
More study is needed, but it is possible that Depo-Provera itself causes a susceptibility to STDs, said Charles Morrison of Family Health International in Research Triangle Park, N.C., who led the study.
“We did adjust for differences in condom use, differences in multiple partners, differences in the number of sexual coital acts,” Morrison said in a telephone interview.
Inner-city and younger women also had a higher risk of STDs, but using Depo-Provera added to the risk, study study found.
Increased use in Africa
Morrison said the researchers were especially concerned because Depo-Provera or its generic equivalent are being increasingly used in Africa, where STDs such as the AIDS virus are very common.
He said women who use Depo-Provera to prevent pregnancy should take extra care if they are in relationships in which either they or their partner have sex with other people.
Like birth control pills, Depo-Provera provides no protection from an infection such as syphilis, gonorrhea or the AIDS virus.
“For sexually active women not in a mutually monogamous relationship, limiting the number of partners may also help to reduce the risk,” Morrison added.
The researchers studied about 800 women age 15 to 45 using two clinics in the Baltimore area -- one urban, serving mostly black women, and one suburban with a client base of white, college-age women. Most were single.
The women chose whether they wanted to use Depo-Provera, contraceptive pills, or a non-hormonal contraceptive method.
After a year, 45 women had become infected with chlamydia or gonorrhea.
The women using the injected contraceptive were three times as likely to have one of the STDs, the researchers said.
No similar risk from birth control pills
Women taking the pills did not have a higher risk of getting an STD, the researchers report in the September issue of the journal Sexually Transmitted Diseases.
Because there were different numbers of women in each group, the researchers calculated risk of infection by “women-years” -- how many women became infected in the space of a year.
The risk for women taking oral contraceptives was 3.9 infections per 100 women-years, 13.7 per 100 women-years in the Depo-Provera group and 6 per 100 women-years in the women using condoms, diaphragms or other non-drug birth control methods.
Morrison said although it appeared from looking at the bare numbers that the pill group had the lowest risk, in fact when other factors were considered their risk of STDs was about the same as the women who did not use hormonal contraception.
Depo-Provera is made by Pfizer Inc. and last month Israel’s Teva Pharmaceutical Industries Ltd. won U.S. approval for a generic version.