Simvastatin belongs to a group of medicines known as statins (or HMG-CoA reductase inhibitors). It regulates the amount of cholesterol and other lipids made by your body. It does this by blocking the action of a certain enzyme (called HMG-CoA reductase) which your body needs to make the fats. This lowers your risk of heart and blood vessel disease. It can also reduce this risk, even if your cholesterol levels are normal, if you are at an increased risk of heart disease as a result of other healthcare problems (such as if you have diabetes mellitus).