Longitudinal trends in polydrug use among young injection drug users

Introduction: Polydrug use is a high risk practice associated with adverse health outcomes. In cross-sectional studies, ketamine abuse has been shown to be associated with high levels of polydrug use. Longitudinal research has been limited, particularly among young injection drug users (IDUs). Methods: We recruited a sample of 67 IDUs aged 16 to 28 who injected ketamine at least once in the previous two years. We conducted three to six interviews with these IDUs over a two-year period, asking about use of ketamine and other drugs. To assess polydrug use, we devised a “multiple drug use” measure, defined as the number of different illegal substances used in the previous 30 days. Results: At baseline, respondents reported using a mean of 3.552 (95% confidence interval: 3.127, 3.977) illegal substances during the previous 30 days. Multiple drug use was similar across gender and age groups. Respondents who reported being HCV positive used a greater number of drugs (mean 4.500). Over the follow up period respondents over age 21 reported a mean decrease of 1.881 substances (95% confidence interval: 1.152, 2.610). Younger respondents showed no such decrease. Rather multiple drug use in this group was characterized by continued high diversity, or intermittent high/low patterns. Gender and HCV status showed no association with longitudinal change in multiple drug use. Conclusion: This longitudinal study indicates that multiple drug use is common among young IDUs who inject ketamine. Polydrug using practices may decrease in prevalence as IDUs mature.