Hormonal contraceptives

A 1999 meta-analysis of 28 studies found a significant association between oral contraceptive pill use and HIV infection, with the strongest effect for studies conducted in Africa (odds ratio 1.65). Studies have tended to be conducted among women at high risk of HIV acquisition, such as commercial sex workers.¹ 

More recently, a ten-year study among high-risk HIV-negative Kenyan women found that use of the DMPA injection (Depo-Provera) was associated with a risk that was 1.8-times greater than women using no hormonal contraceptives. The use of the oral contraceptive pills was associated with a 1.5-times greater risk of HIV infection compared with women not using contraceptives. There were no statistically significant increases in risk for users of implants or non-hormonal intrauterine devices. Other contraceptives were not studied.² 

However a large five-year study conducted in Zimbabwe, Uganda and Thailand found that neither the combined oral contraceptive pill nor DMPA injections were associated with HIV infection. Moreover, contraceptive users who had vaginal infections had no increased risk of infection.³ 

The World Health Organization continues to recommend oral and injectable contraceptives as being appropriate for women at high risk of HIV infection.^{4 5}

Researchers have suggested several possible mechanisms for how hormonal contraception may affect HIV acquisition, including physiological effects on the integrity of the vaginal epithelium, changes in the genital microflora, an increased likelihood of cervical ectopy, an effect on the cell-surface levels of CCR5, which is key to HIV entry, upregulation of HIV gene expression, and hormone use predisposing women to acquire a diverse HIV virus population.⁶

Amongst HIV-positive women, use of hormonal contraceptives may increase genital tract shedding of HIV, which would increase  the risk of HIV transmission. Studies have measured shedding itself, rather than observing infections in the sexual partners of women using contraceptives.

One cross-sectional study found that the infectivity of HIV-positive women was increased by the use of oral or injected contraceptives,⁷ while another cross-sectional study found no such association.⁸ To provide a more definitive answer, investigators conducted a prospective study in Kenya, collecting cervical secretions before and after the initiation of various hormonal contraceptives (combined oral pills, progestin-only pills, DMPA injections). Women starting contraception had a modest but significant increase in the prevalence of HIV infected cells (proviral DNA) and a slight increase in the prevalence of HIV RNA, although this was not statistically significant.⁹