World Health Organization (WHO) guidelines cautioning against oral birth control for HIV-positive women taking antiretrovirals may be overly broad, according to new research that finds some forms may indeed be safe with ARVs. Publishing their findings in the journal Contraception, researchers conducted an open-label, prospective, nonrandomized trial to determine the blood levels of the oral birth control norethindrone in HIV-positive women taking Norvir (ritonavir)–boosted Reyataz (atazanavir).

Some ARVs are believed to reduce the effectiveness of birth control pills. Consequently, WHO and the Centers for Disease Control and Prevention (CDC) have recommended against oral contraceptives for women taking ARVs if other birth control methods, such as barrier devices or IUDs, are available.

There are basically two forms of birth control pills: combination medications that include estrogen and progestin, and methods based just on progestin. Previous studies that led to the WHO and CDC guidelines against combining oral birth controls with ARVs were based only on combination birth control pills. Norethindrone is in the progestin class.

In this new study, 10 HIV-positive women were given norethindrone and Norvir-boosted Reyataz. Another 17 HIV-positive women served as a control group, taking norethindrone along with ARV treatment previously shown not to change levels of norethindrone. All participants took the drugs for 22 days. Blood samples were taken eight times on day 22, the last day of treatment, and then once daily on days 23, 24, and 25 of the study.

As it turns out, Norvir-boosted Reyataz actually raises norethindrone levels when compared with the other ARVs. This suggests that progestin-only, norethindrone-based birth control methods may actually have a higher efficacy among women treated with Norvir-boosted Reyataz. Further research is needed to confirm this, as well as to determine if the same holds true for other forms of progestin.

“It’s important for women to have access to—and the ability to choose from—as wide a range of birth control options as possible,” Ganesh Cherala, an Oregon State University assistant professor of pharmacy practice and a corresponding author on the study, said in a release. “We believe this research shows the WHO guidelines are too generic and unnecessarily cautious. There clearly appear to be oral contraceptives that should be safe and effective in women being treated with HIV medications.”

To read the press release, click here.

To read the study abstract, click here.