Lipitor is classified as a synthetic antihyperlipidemic that acts to lower lipid levels in the body by blocking its ability to synthesize cholesterol. The pharmaceutical agent works by specific inhibition of HMG-CoA reductase, an enzyme that catalyzes the conversion of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) to mevalonate, an early step in cholesterol biosynthesis. By blocking cholesterol synthesis, lipitor reduces the risk of heart disease and/or stroke. When response to diet and other non-drug measures alone are inadequate to reduce cholesterol levels, lipitor is indicated to lower total and LDH cholesterol levels in primary hypercholesterolemia (types IIa and IIb). Side effects include diarrhea, gas, headache, joint pain, nausea, vomiting, and stomach pain.