methadon n synthetic narcotic drug similar to morphine but less habit-forming; used in narcotic detoxification and maintenance of heroin addiction Usage(s) Thousands of heroin addicts have kicked the habit with the help of the synthetic drug methadone. To many of those involved in the fight against heroin addiction, methadone seems to be the most workable weapon yet devised. Methadone, which easily crosses the placental barrier, may impede the fetus's normal development. Synonym(s) methadone methadone hydrochloride dolophine hydrochloride fixer synthetic heroin