Garlic has been used as a medicine for centuries. At first, garlic was used by physicians as a digestive aid. In more recent years, as researchers have isolated and studied individual compounds in garlic, the herb has been touted for its ability to lower cholesterol and blood pressure. Additionally, garlic is sometime promoted as an antibacterial, antiviral and anticancer herb.

Unfortunately, despite several decades of study on garlic and its components, the evidence remains mixed at best. In 2007, the results of one of the best-designed human studies to date were released. This study compared three formulations of garlic in a head-to-head test to see which, if any, was most effective at lowering cholesterol levels. Ultimately, researchers concluded that none of the garlic preparations were effective at lowering cholesterol.

However, these results are contradicted by earlier studies that show garlic can slightly lower cholesterol for the short-term and may have additional heart-healthy benefits, such as slowing the progression of coronary artery disease and perhaps slightly lowering blood pressure. In fact, the benefits of garlic, if any, remain a hotly debated topic, presumably driven by these conflicting study results.

Unfortunately for consumers, there is no scientific consensus on the value of garlic supplements, even while there may be ample anecdotal evidence or a strong tradition of herbal medicine. Fortunately, garlic does not appear to be harmful or have many side effects and can usually be added to the diet without causing hardship. However, it is important that anyone starting a supplementation program first clear it with their physician to make sure there is no risk of interactions with existing prescription drugs or other harmful side effects.

Known side effects of garlic include a pungent odor, upset stomach and possible allergic reactions. Garlic may also act as an anti-platelet and therefore should not be used immediately before surgery or in combination with existing anti-platelet drugs unless under the direct supervision of a physician. Finally, garlic may interact with certain antivirals that are used to treat HIV.