Attenuation of precipitated abstinence in methadone-dependent rats by delta 9-THC.

Racemic methadone hydrochloride was administered to male rats in daily subcutaneous injections of 10-30 mg/kg. Dependence, when assessed by naloxone challenge after 26 days, was quantitatively and qualitatively similar to that previously reported by us for rats implanted with a 75 mg morphine pellet for 72 hours. Abstinence scores in animals pretreated acutely with 10 mg/kg delta 9-THC one hour before naloxone were significantly less than those of a vehicle control group, and wet shakes and gastrointestinal signs of abstinence were blocked. These results extend previous observations of morphine abstinence attenuating properties of delta 9-THC to effects on animals dependent on methadone.