REINFORCING EFFECTS OF A COMBINATION OF ETHANOL AND METHADONE RELATIVE TO EACH DRUG ALONE

Studies report a high incidence of alcohol abuse in methadone maintena nce patients. There is, however, little data on the reinforcing effect s of combinations of ethanol and methadone. In the present study, oral self-administration of a combination of 1% (w/v) ethanol and 0.2 mg/m l methadone was compared to each drug alone in three rhesus monkeys in which methadone alone was not a reinforcer. In Experiment 1, ethanol and the combination, but not methadone alone, served as reinforcers. I n Experiment 2, there was no preference for ethanol or the combination at fixed ratio (FR)8 or 16. When the FR size was doubled (FR 16 or 32 ), all three animals preferred the combination to 1% ethanol. Experime nt 3 further examined the effect of work requirement on preference for ethanol or the combination by varying FR values [1, 2, 4, 8, 16, or 3 2]. At lower FRs, ethanol was significantly preferred to the combinati on. As FR was increased, there was a significant reduction in preferen ce for ethanol over the combination. The results show that an ethanol + methadone combination will be orally self-administered by monkeys an d suggest that work requirement differenetially modifies preference fo r the combination and ethanol alone. (C) 1998 Elsevier Science Inc.