Do you fit this description: You have both HIV and hepatitis B (HBV), don’t need to take HIV meds but do need treatment for hep B? If so, avoid the new HBV med Baraclude (entecavir)—at least for now. A recent study by researchers at Johns Hopkins School of Medicine in Baltimore showed that Baraclude suppresses HIV along with HBV.

That may sound good, but it means that taking Baraclude solo—without additional HIV meds—could allow your HIV to become resistant to the drug and other nukes. (HIV monotherapy can lead to drug resistance.) That, in turn, could limit your choices when you do begin HIV meds. Scientists originally thought Baraclude suppressed HBV but not HIV, setting it apart from some other HBV drugs (Hepsera and Epivir-HBV), which attack both viruses.

The new data prompted Bristol-Myers Squibb, maker of Baraclude, to alert HIV docs to the problem in February. But BMS’s Richard Colonno, PhD, says that more investigation is needed. In ten years of testing Baraclude, Colonno says, BMS never found evidence that it suppresses HIV. BMS and Hopkins researchers will team up to resolve the conflict.