In addition to these clinical studies, the review's authors examined animal, cell and biochemical research on the form of progestin used in DMPA—medroxprogesterone acetate, or MPA. The analysis revealed MPA acts differently than other forms of progestin used in contraceptives. MPA behaves like the stress hormone cortisol in the cells of the genital tract that can come in contact with HIV.
"The increased rate of HIV infection among women using DMPA contraceptive shots is likely due to multiple reasons, including decreases in immune function and the protective barrier function of the female genital tract," Hapgood said. "Studying the biology of MPA helps us understand what may be driving the increased rate of HIV infection seen in human research. These findings suggest other forms of birth control should rapidly replace DMPA shots."