For some people, MDMA can be addictive. According to NIDA, 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. MDMA affects many of the same neurotransmitters 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.
The potential adverse effects of MDMA on the developing fetus are of great concern. Behavioral studies in animals have found that fetal exposure to MDMA can have significant adverse effects on learning and memory. echoua.com
There was also rising concern that ecstasy for many young people was the gateway to other hallucinogens like LSD and other drugs like cannabis and heroin to chill out after ecstasy use.
UNODC Regional Centre Project AD/RAS/97/C5/THA "The Enhancement of Drug Law Enforcement Computer-based Training in East Asia ", Drug Identification DVD.
U.S Department of Health and Human Services - National Institute on Drug Abuse: Research Report Series. MDMA (Ecstasy) Abuse, 2004.