Patients undergoing opioid-agonist therapy (OAT) who were cannabis users were more likely to drop out of treatment, a Canadian retrospective cohort study showed.

Canada has passed legislation that will lead to legalization of cannabis for recreational use. Researchers disagree about the public health effects that legalization will have. Alexandra M. Franklyn and her coinvestigators at the Northern Ontario School of Medicine, Sudbury, designed their study to look at one population that might be at risk of cannabis-related harms.

Patients studied had initiated first-time OAT in any of 58 addiction treatment centers in Ontario between Jan. 1, 2011, and June 17, 2012, with methadone and possible transition to buprenorphine/naloxone, and were older than 15 years. Discontinuation was defined as not receiving a dose of either OAT drug for 30 days. Baseline use of cannabis was defined as one positive urine test within the first 30 days, and heavy use was defined as 75% or more of a patient’s tests being positive for the duration of the study.

Of 644 patients, 328 (50.9%) were baseline cannabis users. Baseline users were 38.9% more likely to drop out of OAT. Heavy cannabis users (n = 256; 39.8%) were 48.1% more likely to drop out of OAT than those who weren’t heavy users. Heavy users are “a group that should be carefully monitored throughout treatment,” regardless of whether the cannabis use can be considered another substance use disorder or if it is intended to self-medicate another condition that may make dropout more likely, Ms. Franklyn and her colleagues concluded.

“While studies have shown a potential for cannabis legalization to be a positive change for the population as a whole, there may be unique implications for those patients receiving OAT. … These patients should receive education surrounding the potential harms of cannabis use, including worsened OAT outcomes,” the researchers wrote ( PLoS One. 2017 Nov 8;12[11]:e0187633 ).

Neither Ms. Franklyn nor her colleagues had conflicts of interest to disclose.


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