Medical marijuana, more appropriately called cannabis, may be used as a harm reduction agent to combat the opioid epidemic. A study published in 2014 found that in states with a medical cannabis law there was a 24.8% lower incidence of opioid overdose deaths compared to states where cannabis remains illegal (Bachhuber et al., 2014).

Cannabis is an ancient herbal medicine and was one of the most popular medicines in the United States prior to the Marihuana Tax Act of 1937, which marked the beginning of cannabis prohibition. Cannabis is an effective medicine for neuropathic pain, and pain management is the most common use of cannabis in the states that currently allow the use of medical cannabis.

When used as an adjunct to opioids for pain management, cannabis works synergistically with opioids to provide pain relief. Research shows that patients who use cannabis can use a lower dose of an opioid and that tolerance to the opioid develops more slowly (Cichewicz, 2004; Abrams et al., 2011). In addition, cannabis can help alleviate opioid withdrawal symptoms, leading some clinicians to call cannabis an exit drug (Lucas, 2012; Reiman, 2009).

Unfortunately, many clinicians include the active ingredient of cannabis, tetrahydro­cannabinol (THC), in the urine drug screen panels for patients prescribed opioids. While drug screens can be clinically useful to ensure that the patient is using the prescribed opioid and to ensure other opioids or drugs, such as benzodiazepines, are not used illicitly (due to potential overdose from the combination), the illicit use of cannabis is not necessarily of clinical concern. The 2016 CDC guidelines cited earlier call for urine drug screening (recommendation 10), but note that

Clinicians should not test for substances for which results would not affect patient management or for which implications for patient management are unclear. For example, experts noted that there might by uncertainty about the clinical implications of a positive urine drug test tor tetrahydro­cannabinol (THC). (Dowell et al., 2016)