Garlic supplements can cause a potentially harmful side effect when combined with a type of medication used to treat HIV/AIDS. Investigators from the National Institutes of Health have found that garlic supplements sharply reduced blood levels of the anti-HIV drug saquinavir. The study appeared recently in the online edition of Clinical Infectious Diseases.

Researchers found that the blood level of saquinavir, one of a class of drugs called protease inhibitors that slow progression of HIV infection, dropped an average of 51 percent in those who took garlic supplement.

And after a 10-day period without the garlic, the blood level of saquinavir was still lower than expected.