Patterns of smoking and injecting methamphetamine and their association with health and social outcomes

INTRODUCTION: We examine how smoking and injecting methamphetamine change over time and correlate with specific health and social outcomes. METHODS: Panel data from a longitudinal cohort dependent on methamphetamine (N = 444; 891 months). Random effects regression models examined the relationship between smoking and/or injecting methamphetamine and past month outcomes (substance use, ≥daily injection, needle/syringe sharing, psychological distress, poor mental and physical health, sexual behaviour, psychotic symptoms, violent behaviour and crime). Effects were adjusted for between‐group differences at baseline. RESULTS: At baseline, 56% of participants only injected methamphetamine in the past month, 18% only smoked and 26% both injected and smoked (concurrent injecting and smoking). Compared to injecting only, concurrent injecting and smoking was associated with more days of methamphetamine use (b = 1.3, P < 0.001; adjusted [A] b = 1.2, P < 0.001), more frequent injection [odds ratio (OR) 1.8, P = 0.013; adjusted OR (AOR) 1.6, P = 0.042], violent behaviour (OR 2.1, P = 0.001; AOR 1.8, P = 0.013] and crime (OR 3.1, P < 0.001; AOR 2.5, P < 0.001). Non‐injecting related outcomes did not differ significantly for only smoking versus only injecting. There was no significant transition from injecting methamphetamine at baseline to non‐injecting methamphetamine use at follow up, or from exclusively smoking methamphetamine at baseline to any methamphetamine injection at follow up. DISCUSSION AND CONCLUSION: Efforts are needed to address heavier methamphetamine use, more frequent drug injection and elevated violent behaviour and crime among people who concurrently smoke and inject methamphetamine.