Cannabis may have serious interactions with some drugs. It is recommended that clinicians privilege non-interacting alternatives where clinically feasible. Examples of serious interactions with cannabis include:
- Warfarin: Smoked cannabis may inhibit the metabolism of warfarin (CYP2C9 substrate), resulting in increased international normalized ratio and risk of bleeding.
- Clopidogrel: Since cannabis inhibits CYP2C19, concomitant use leads to subtherapeutic concentrations of clopidogrel. This decreases its protective effects on cardiovascular disease and events.
- Clobazam: Increased risk of benzodiazepine toxicity.
- CNS depressants and sympathomimetics: Additive effects
- Theophylline, clozapine, and olanzapine: Reduced efficacy
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