For some people, MDMA can be addictive. A survey of young adult and adolescent MDMA users found that 43 percent of those who reported ecstasy use met the accepted diagnostic criteria for dependence, as evidenced by continued use despite knowledge of physical or psychological harm, withdrawal effects, and tolerance (or diminished response), and 34 percent met the criteria for drug abuse. Almost 60 percent of people who use MDMA report withdrawal symptoms, including fatigue, loss of appetite, depressed feelings, and trouble concentrating.³⁴

MDMA affects many of the same neurotransmitter systems in the brain that are targeted by other addictive drugs. Experiments have shown that animals prefer MDMA, much like they do cocaine, over other pleasurable stimuli, another hallmark of most addictive drugs.³⁵