Users say meth creates a feeling of euphoria along with increased energy and reduced appetite. A psychostimulant, meth is highly addictive despite, or perhaps, because of the fact that it causes profound and long-lasting damage to the brain. Post-mortem studies link the drug to diseases of aging, including coronary atherosclerosis (hardening of the arteries) and pulmonary fibrosis (scar tissue in the lungs). Something is happening at the cellular level to cause these strange physical effects, but what is it?