Monacolin K is a natural compound found in fermented red rice, particularly in the product known as red yeast rice. It is known for its ability to help lower cholesterol levels by inhibiting the enzyme HMG-CoA reductase, which plays a key role in cholesterol production in the liver. Research suggests that Monacolin K can be effective in managing cholesterol levels, similar to some prescription medications. However, the concentration of Monacolin K can vary in different red yeast rice products, making it important for consumers to choose high-quality supplements and consult healthcare professionals before use.