Concomitant use of medical cannabis and drugs associated with risks of interaction in older patients: a longitudinal cohort study.

BACKGROUND

Cannabinoids interact with multiple drugs, with some interactions having significant clinical effects.

OBJECTIVES

This study aimed to evaluate amongst older people (i) the trends in the concomitant medical use of cannabis and drugs associated with a risk of significant clinical interaction with cannabinoids (DARSCIC), including those with a narrow therapeutic index (drugs with a narrow therapeutic index; DNTI) such as warfarin, and (ii) the risk of bleeding, drug-related intoxication, thyrotoxicosis and major cardiovascular events.

METHODS

For objective 1, we conducted an interrupted time series study amongst 12 599 seniors who received an authorised cannabis prescription in Ontario from 2014-2019. Using clinical and medico-administrative data, dispensations of DARSCIC were assessed pre-post cannabis prescription. For objective 2, longitudinal cohort studies were conducted in patients concomitantly exposed to cannabis and warfarin (bleeding) or to DNTI (intoxication) versus controls.

RESULTS

For objective 1, the trends of DARSCIC/DNTI dispensations were similar in the year before and after cannabis prescription. For objective 2, amongst 378 patients exposed to cannabis and warfarin, the risk of bleeding was 1.19, 95%CI (0.71-1.98), compared to 1646 controls. The risk of drug-related intoxication was 2.61, 95%CI (1.42-4.79) amongst 3926 patients exposed to cannabis and DNTI compared to 12 223 controls. Patients exposed to cannabis and levothyroxine (n = 2499) had a significantly higher risk of heart failure but not thyrotoxicosis, acute coronary syndrome or stroke.

CONCLUSION

These findings indicate that prescribing practices for cannabis may not adequately consider the implications of DARSCIC/DNTI. Enhancing prescriber awareness of these interactions could mitigate the risk of adverse effects such as drug-related intoxication.