A method for measuring the severity of multi-drug use among psychiatric patients has been developed which takes into consideration the three basic criteria of drug abuse: number of different drugs used, frequency of use and length of use. The procedure initiated with several mental health professionals rating the drug-use patterns of 117 young psychiatric patients with a history of drug abuse. These ratings were then used to develop scoring criteria for each individual drug and combinations of drugs. The final result is a method which systematically categorizes drug users as either mild, moderate or heavy users.