Cannabis is an herbal drug. Although the level of danger from mixing cannabis with prescription medications is significantly lower than the risk from mixing with alcohol, cannabis can interact negatively with various medications, leading to potentially harmful effects.
Several medications are metabolized by the same liver cytochrome enzyme systems as cannabis. Cannabis is a CYP3A4 inhibitor, which can lead to decreased metabolism of a broad range of medications if taken with cannabis. Cannabis also interacts with the CYP2C9, CYP2B6, CYP1A2, CYP2C19 systems, although those interactions may sometimes lead to increased metabolism of some drugs or even to an increased blood level of cannabis. Here are just a few common medications that may have significant interactions with cannabis:
Anticoagulants: Cannabis can increase the risk of bleeding when taken with warfarin. THC and CBD may increase the level of Warfarin in the blood stream through the CYP2C9 enzyme.
Sedatives, Anti-Anxiety, and Opioid Medications: Although not directly related to metabolism, combining cannabis with sedatives, anti-anxiety medications, or prescription pain relievers can enhance the sedative effects and increase the risk of drowsiness and respiratory depression. There are more than a few healthcare providers who will not prescribe Benzodiazepines such as Xanax (Alprazolam), or opiates, such as Vicodin (Hydrocodone with Acetaminophen), if the patient uses cannabis.
Antidepressants and other Psychotropics: Cannabis may interact with certain antidepressants, potentially leading to increased side effects or reduced efficacy. The blood level of Emsam (Selegiline), a CYP2B6 substrate, an antidepressant and Parkinson’s Disease treatment, may be increased by THC. Conversely, Clozaril, an anti-psychotic and CYP1A2 substrate, may be cleared from the blood stream faster in the presence of THC, decreasing the blood level, which could cause worsening of symptoms.
Anticonvulsants: Cannabis can interact with medications used to treat epilepsy, potentially altering their effectiveness. The blood level of a metabolite of Clobazam may be increased to dangerously high levels, through the CYP2C19 enzyme, which could lead to adverse effects. Tegretol (Carbamazepine), a CYP2C9 inducer, increases the level of cannabis, but cannabis does not affect the level of Carbamazepine.
Immunosuppressant Medications: Cannabis increases the levels of Tacrolimus, Cyclosporin, and other anti-rejection medications, via CYP3A4, leading to a risk of toxicity and other severe adverse effects.
Anti-infection medications: Interestingly, there are a few medications in this class that increase the levels of THC and/or CBD. Rifampin, a CYP3A4 inducer, used to treat tuberculosis, decreases the levels of THC and CBD, which could be important for medical cannabis users. Sulfamethoxazole, commonly used to treat urinary tract infections and a CYP2C9 inhibitor, may increase THC levels, although it does not increase CBD levels. Ketoconazole, used to treat fungal infections, significantly increases THC and CBD levels.
It’s important to let your healthcare provider know that you use cannabis, even if you are not an habitual user. One should also disclose the use of any other herbal products or nutritional supplements.
Here is a tool to help you to find out if your medication may interact with cannabis:
Sources used and for more in-depth information:
