This study aimed to explore the incidence of adverse events (AEs) reported by patients when initiating medicinal cannabis treatment for chronic pain, and the association of cannabis constituents, dose and concomitant medicines with AE incidence.
Patient demographics, cannabis products and AE data were collected as part of the Cannabis Access Clinics Observational Study, and concomitant medicines were obtained from patient health summaries provided by referring doctors. Cannabis products were grouped by their constituents as either cannabidiol-only or containing both cannabidiol and Δ-9-tetrahydrocannabinol.
From a total of 275 patients, each had a median of six concomitant medicines, with opioids (n = 179; 65%) the most common. A total of 35.6% patients took 10 or more other medicines, and they were associated with a 3.6 times higher likelihood to report the AE of fatigue (P = 0.048). Patients who received concomitant gabapentinoids were 2.4 times more likely to report dizziness (P = 0.036), patients on tricyclic antidepressants were 1.8 times more likely to report somnolence (P = 0.034) and 3.4 times more likely to report anxiety (P = 0.04), when compared with patients who were not prescribed those classes of medications. Those patients who were prescribed products containing both cannabidiol and Δ-9-tetrahydrocannabinol were 1.5 times more likely (P = 0.004) to have experienced an AE when compared with those prescribed only cannabidiol.
These findings show that certain concomitant medications and cannabis constituents may be associated with AE incidence when initiating medicinal cannabis. These potential pharmacokinetic and pharmacodynamic interactions require further study to develop guidance for prescribers and pharmacists.