A federally funded review of research on garlic supplements has found that they may lead to small reductions in the total cholesterol level, but only for a short time.

Compared with placebo, garlic preparations were associated with small reductions in total cholesterol at 1 month (1.2 - 17.3 mg/dL) and at 3 months (12.4 - 25.4 mg/dL), but not at 6 months. Changes in LDL and triglyceride levels were similar. There were no statistically significant differences in HDL. The study also reported no effect on glucose levels and insignificant effects on blood pressure.

Proven adverse effects included malodorous breath and body odor; less well documented effects included flatulence, pain in the esophagus and abdomen, allergic reactions, and bleeding.