DDIs are classified broadly by mechanism. Pharmacokinetic interactions affect the absorption, distribution, metabolism, or excretion (ADME) of one or both substances , most commonly through induction or inhibition of cytochrome P450 (CYP) enzymes in the liver. Pharmacodynamic interactions occur when two substances act at the same receptor or physiological pathway, producing additive, synergistic, or antagonistic effects without altering either substance's plasma concentration.
Clinical significance varies widely. Some DDIs are well-characterised and predictable from known receptor pharmacology; others emerge only through post-market surveillance or spontaneous adverse-event reporting. The Therapeutic Goods Administration (TGA) requires sponsors to characterise known DDI risk as part of the Australian registration dossier, and prescribers are expected to consult product information (PI) documents when co-prescribing. Under the Poisons Standard (the current Standard for the Uniform Scheduling of Medicines and Poisons), scheduling decisions can be influenced by a substance's known interaction profile.
In the context of cannabinoids, the CYP2C9 and CYP3A4 pathways are of particular research interest, as these enzymes are responsible for metabolising a range of prescription medicines. Peer-reviewed literature , including work indexed on PubMed/NCBI , continues to characterise the interaction profile of plant-derived and synthetic cannabinoids with anticoagulants, antiepileptics, and other scheduled medicines, though many studies to date involve small samples and carry significant methodological limitations.
Consumers and practitioners seeking Australian-specific DDI guidance should consult the TGA's published product information, the NPS MedicineWise interaction checker, or refer to a registered pharmacist or medical practitioner. Self-managing a potential DDI without professional advice carries documented clinical risk.
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