If you take a red yeast rice supplement to lower your cholesterol, be aware that the amount of its key active ingredient may vary by as much as 120-fold, according to a study in the European Journal of Preventive Cardiology, which analyzed 28 brands. The ingredient is monacolin K, which in purified form is actually a statin drug (lovastatin).
At the low end, you would get virtually no monacolin K; at the upper end, you would get the equivalent of the lowest daily dose of prescription lovastatin (10 milligrams).
Used in traditional Chinese medicine, red yeast rice is made by fermenting rice with yeast—a process that can yield widely variable end-products. These supplements may also contain other compounds (including other monacolins) that could affect cholesterol and have additional bioactive effects in the body.
Bottom line: “Natural” in this case means “unpredictable”—you have no way of knowing what is in the bottle and what effect (good, bad, or none) it will have. There’s no reason to take red yeast rice supplements when generic statins are inexpensive, standardized, and effective.
Also see Cholesterol-Lowering Supplements.