The active ingredient in a drug used to lower the amount of cholesterol in the blood and to prevent stroke, heart attack, and angina (chest pain). It is also being studied in the prevention and treatment of some types of cancer and other conditions. Atorvastatin blocks an enzyme that helps make cholesterol in the body. It also causes an increase in the breakdown of cholesterol. It is a type of HMG-CoA reductase inhibitor and a type of statin.