As with any other medication, drug interactions should be checked before a patient starts a medical cannabis regimen. Owing to the need for more research, the fundamental ambiguity of the endocannabinoid system, and the wide range of pharmacologically active compounds potentially present in any cannabis formulation, it is very difficult to definitively list drug interactions. It is important to note that there are numerous pertinent compounds in cannabis, and they need to be specifically examined for how they interact with other pharmaceuticals.

Cannabis is suspected to decrease platelet aggregation, induce CYP2E1, inhibit CYP3A4 and P-glycoprotein, and function as a CNS depressant. Patients should be cautious using cannabis while they are taking CNS depressants, anticholinergics, or sympathomimetics due to potential increased chances of side effects. THC is metabolised by CYP2C9 and CYP3A4, while CBD is metabolized by CYP2C19 and CYP3A4. Medications which inhibit these enzymes can increase the plasma concentrations of THC and CBD, leading to adverse effects. Conversely, a potent inducer of these enzymes can render the cannabis dose ineffective. There is the potential for cannabis to cause hypomanic events in patients who are taking disulfiram or fluoxetine.The evidence for this interaction comes from the Marinol® drug trials in which two case reports (one for each medication) detailed this adverse effect. While it may not be of importance to most patients on these medications, special care should be used in patients that suffer from bipolar disorder or are prone to manic events. Modification of prescription dosages may need to be considered through assessment of the effects of the medical cannabis.

To read more about drug interactions and medical cannabis purchase Cannabis Primer: An Introduction to Cannabis for Consumers, Producers, Providers, Policy Makers, and Health Professionals