Although we present data from the longest time period possible, methodological changes in the NSDUH preclude examination beyond 2014, and thus how trends in illegal behaviors and sources of non-medical opioids have changed in more recent years is not known. As with any observational study, causal relationships cannot be inferred. However, our findings provide important information on changes in behaviors on a population level over time. Finally, as NSDUH excludes persons who are currently incarcerated, our prevalence data for justice system involvement are likely underestimates.
