Glossary
Drug–drug interaction (DDI)
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When one medication changes the effect, level, or safety profile of another — central to safe cannabinoid co-prescribing.
A drug–drug interaction (DDI) occurs when one medication alters the pharmacological effect of another — by changing absorption, distribution, metabolism, excretion, or by competing at the same target receptor. DDIs can be **pharmacokinetic** (changing drug levels, often through CYP450-mediated metabolism) or **pharmacodynamic** (additive or opposing effects on the same physiological system).
**Cannabinoid-specific DDI considerations:** - **Pharmacokinetic** — both THC and CBD inhibit several CYP450 isoforms (especially CYP3A4, CYP2C9, CYP2C19), which can raise levels of warfarin, clobazam, tacrolimus, certain antidepressants, and statins. - **Pharmacodynamic** — additive sedation with benzodiazepines, opioids, or alcohol; additive orthostatic effects with antihypertensives; additive cognitive effects with anticholinergics.
**Safe-prescribing strategy** — comprehensive medication review at every cannabinoid initiation, pharmacist sign-off where the medication list is complex, monitoring (warfarin INR, clobazam levels, LFTs, blood pressure), and structured dose-staging where interaction is predictable. Many DDIs are predictable and manageable; some make cannabinoid co-prescribing inappropriate. The doctor will not initiate without working through this list.
Related terms
- CYP450Family of liver enzymes that metabolise many drugs, including cannabinoids — source of many clinically relevant interactions.
- CYP3A4Most abundant hepatic CYP450 isoform; affected by both THC and CBD.
- CYP2C9CYP450 isoform that metabolises warfarin and NSAIDs; inhibited by CBD and THC.
- THC (Δ⁹-tetrahydrocannabinol)The principal psychoactive cannabinoid in the cannabis plant.
- CBD (cannabidiol)Non-psychoactive cannabinoid with established use in some seizure disorders and emerging use in anxiety.