Cholesterol producing enzyme and statin. Computer model showing the molecular structure of HMG-CoA reductase (HMGCR) in complex with Atorvastatin. HMGCR is is the rate-controlling enzyme of the metabolic pathway that produces cholesterol in the body. Atorvastatin is a member of the group of drugs known as statins, which are used for lowering blood cholesterol. Like all statins it works by inhibiting the action of HMGCR.