Current World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) guidelines caution HIV-positive women taking antiretrovirals (ARVs) not to use oral contraceptives if other birth control methods are available, because some ARVs are thought to reduce their effectiveness. However, new research finds that some forms of oral birth control may indeed be OK to use with ARVs, suggesting that these guidelines may be overly broad.

There are basically two forms of birth control pills: combination medications that include estrogen and progestin, and methods based just on progestin. The previous studies that informed the WHO and CDC guidelines were based only on combination birth control pills.

Researchers examined the blood levels of the oral birth control norethindrone, a progestin, in HIV-positive women taking Norvir (ritonavir)-boosted Reyataz (atazanavir), and compared them with a group taking norethindrone along with ARVs previously shown not to change levels of the contraceptive. As it turns out, boosted Reyataz actually raises norethindrone levels compared with the other ARVs.

“Researchers and practitioners have been extrapolating data from these other formulations [of contraceptives and ARVs] and applying them to this particular formulation,” says Ganesh Cherala, PhD, an assistant professor of pharmacy practice at Oregon State University, who was a corresponding author on the study. “For the first time we have data that that extrapolation actually doesn’t make sense.”

Future research is still needed to determine if the raised levels of the birth control pills would make them more effective.