We propose a longitudinal, prospective cohort study to determine if changes in cannabis use frequency are associated with changes in frequency of opioid use and drug-use related health outcomes among opioid- using (both heroin and prescription opiates) people who inject drugs (PWID) in two states with legal adult cannabis sales and use. State-level legalization of adult cannabis sales and use is likely to lead to greater cannabis use and cannabis-related health problems among vulnerable populations. However, increases in cannabis sales and use might have unanticipated consequences for PWID. Preliminary studies suggest substitution of cannabis for opioids among medicinal cannabis patients and community recruited PWID. Ecological studies have found that medical marijuana legalization is associated with lower rates of opioid- related overdose and hospitalization, outcomes that might be observable for legal adult use cannabis. Based on these findings, we theorize that cannabis use may reduce opioid use and thereby lower the risk for opioid- related drug harms such as nonfatal overdose events. Therefore, we propose the following aims:
AIM 1 : To determine whether changes in cannabis use are associated with changes in frequency of opioid use among opioid-using PWID while adjusting for confounders. Hypothesis 1 (H1): The rate of change in cannabis use over time will be inversely associated with the rate of change in opioid use during the same period.
AIM 2 : To determine whether changes in cannabis use among opioid-using PWID is associated with changes in non-fatal overdose events while adjusting for confounders. H2: The rate of change in cannabis use will be inversely associated with the rate of change in the number of non-fatal overdose events. To achieve these aims, we propose to recruit, interview, and follow at baseline, 6 and 12 months a prospective, longitudinal cohort of 1,000 opioid-using PWID in Denver, CO (N=500) and Los Angeles, CA (N=500). Opioid-using PWID will be recruited using targeted sampling methods. Multiple observation periods and large sample size will permit the use of cutting edge statistical techniques such as latent growth modelling and finite mixture modelling to rigorously test our hypotheses. Our two sites allow us to observe drug use patterns and health outcomes among racially/ethnically diverse PWID. The prevalence of non-fatal overdoses has increased in recent years. In our 2016/17 sample of Los Angeles PWID (n=472), 21% reported a non-fatal overdose in the last 6 months, meaning the proposed sample should have sufficient non-fatal overdoses events to permit statistical analyses of changes over time as proposed here. Findings will advance drug use epidemiology and may inform new prevention programs for the reduction of drug-related harms. Our study team is multidisciplinary (economics [Pacula], epidemiology [Corsi, Kral], psychology [Booth & Huh], and sociology [Bluthenthal]) and well-prepared to conduct this significant, innovative, and rigorous 4-year research project.

Public Health Relevance

The overall goal of this project is to examine the drug use impacts and health outcomes of cannabis use on opioid-using people who inject drugs (PWID) in Denver, Colorado and Los Angeles, California. This will be accomplished by collecting data on drug use patterns and health ailments among 1,000 opioid-using PWID (500 at each site) in three interviews over the course of 12 months. Legalization of adult use cannabis sales continues to grow at the state level in the United States. The impact of increased legal cannabis sales on special populations such as PWID has not been studied. Public health consequences of changes in cannabis use among PWID will be documented and analyzed.

National Institute of Health (NIH)
National Institute on Drug Abuse (NIDA)
Research Project (R01)
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Addiction Risks and Mechanisms Study Section (ARM)
Program Officer
Kimmel, Heather L
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University of Southern California
Public Health & Prev Medicine
Schools of Medicine
Los Angeles
United States
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