Morphinelike arousal by methadone during sleep

Methadone was investigated to see if it induced an insomnia comparable to that after single doses of morphine. After one adaptation night, the sleep of seven male nondependent opiate addicts was studied after intramuscular methadone (7.5, 15, or 30 mg/70 kg), morphine (10 or 20 mg/70 kg), and placebo at weekly intervals in a randomized double-blind crossover design. Drug effects were measured on several sleep and wakefulness patterns. Methadone is equipotent to morphine in its increase of wakefulness, drowsiness, muscle tension, shifts in sleep-waking state, and latency to rapid eye movement sleep (REMS) and its decrease of sleep efficiency, delta sleep, and REMS. This similarity of methadone to morphine in acute arousal from sleep is in contrast to the differences between these two drugs during long-term administration, when morphine induces a small but persistent arousal and methadone does not.