Is Cannabis being used as a substitute for non-medical opioids by adults with problem substance use in the United States? A within-person analysis.

Among US adults with problem substance use who use non-medical opioids, the odds of opioid use appear to be approximately doubled on days when Cannabis is used. This relationship does not appear to differ between people with moderate or more severe pain versus less than moderate pain, suggesting that Cannabis is not being used as a substitute for illegal opioids.