Nonreporting of cannabis use: Predictors and relationship to treatment outcome in methadone maintained patients

Underreporting of drug use is common and influenced by multiple factors. Cannabis (THC) use nonreporting and its relationship to heroin and cocaine use were investigated in 690 patients enrolled in 25- to 29-week clinical trials of contingency management plus methadone maintenance. Urine specimens and self-reports of drug use were collected 3 times/week. Potential predictors of THC use nonreporting were analyzed by multiple logistic regression; relationships between THC use nonreporting and % cocaine- and opiate-positive urines were analyzed by multiple regression. Compared to non-THC users (n = 317), patients with THC-positive urines (n = 373) were more likely to be male and have more years of THC use, but were not different on other characteristics. Nonreporting to user ratios were: THC 191/373 (51.2%); opiates 17/686 (2.5%); cocaine 21/681 (3.1%). Predictors of THC use nonreporting were low rate of THC-positive urines during treatment, fewer days of THC use in the last 30 before treatment, African-American race, and absence of antisocial personality disorder. Nonreporting of THC use was associated with significantly greater opiate and cocaine use. Contingency management decreased cocaine use in THC nonreporters to the level of reporters. Nonreporting of THC use is a significant predictor of greater cocaine and heroin use. This association can be eliminated with contingency management therapy.