Questions remain about a safe and effective dose and what form of garlic you should consume. Eating garlic as a food may reduce its effectiveness, apparently because your stomach breaks down allicin, the sulfur-containing compound responsible for much of garlic's health benefits. Fresh garlic may lose its effectiveness quickly after you cut or crush it. And cooking may either decrease or increase the potency of various compounds in garlic. Taking very large amounts of garlic may cause anemia and irritation of your intestinal tract.
Many people consider garlic's odor offensive.
One solution is to use odorless, enteric-coated garlic tablets. The coating allows the tablet to pass through your stomach intact so that the garlic can be absorbed by your small intestine. Some researchers use aged garlic extract, which contains possibly more effective sulfur compounds than those found in fresh garlic. However, two studies showed no benefits from garlic extract. Like vitamin E, no official medical organization has endorsed the use of garlic for preventing heart disease.