Medical cannabis can interact with many prescription and over-the-counter medications, especially those processed by the liver's cytochrome P450 enzymes. The most common interactions involve blood thinners, anticonvulsants, antidepressants, antipsychotics, opioids, benzodiazepines, and other central nervous system depressants. Because THC and CBD can change how these drugs are broken down, side effects may increase or the medication may stop working as intended.
Why Medical Cannabis Interacts With Medications
Your liver uses enzymes, mainly the cytochrome P450 family, to break down most medications. THC and CBD are also processed by these enzymes. CBD is a strong inhibitor of several CYP enzymes, including CYP3A4 and CYP2D6. THC has a weaker effect. When you take medical cannabis with another drug, the cannabis can slow that drug's breakdown, raising its level in your blood. This can lead to more side effects. In some cases, cannabis can also speed up the breakdown of a drug, making it less effective.
Medications That May Interact With Medical Cannabis
The following drug classes are most often linked to cannabis interactions. This list is not complete. Always check with your prescriber or pharmacist.
medical cannabis drug interactions list
- Blood thinners: warfarin, apixaban, rivaroxaban, clopidogrel. Cannabis may increase bleeding risk or change INR.
- Anticonvulsants: clobazam, valproate, carbamazepine, phenytoin. CBD can raise levels of clobazam's active metabolite.
- Antidepressants: fluoxetine, sertraline, amitriptyline. Combining with cannabis may increase drowsiness or dizziness.
- Antipsychotics: clozapine, olanzapine, risperidone. Cannabis may increase sedative and metabolic side effects.
- Opioids: morphine, oxycodone, fentanyl. Cannabis can add to sedation and slow breathing.
- Benzodiazepines: diazepam, alprazolam, lorazepam. Increased risk of extreme drowsiness and falls.
- Statins: simvastatin, atorvastatin, lovastatin. Higher levels may raise the risk of muscle damage.
- Immunosuppressants: tacrolimus, cyclosporine. These drugs have a narrow safety range, so small changes matter.
- Heart medications: beta-blockers, calcium channel blockers. Cannabis can affect heart rate and blood pressure.
- Diabetes medications: insulin, metformin. Cannabis may affect blood sugar control.
- Antihistamines and muscle relaxants: diphenhydramine, cyclobenzaprine. Additive sedation is common.
How to Reduce Interaction Risks
You can lower your risk by working with your healthcare team.
is it safe to mix cannabis with medications
- Tell every doctor and pharmacist that you use medical cannabis. Include the product, dose, and how you take it.
- Start with a low dose of cannabis and increase slowly. This helps you notice side effects early.
- Keep a written list of all medications, including over-the-counter drugs and supplements.
- Avoid alcohol and other sedatives when using cannabis. The combined effect can be dangerous.
- Ask your doctor if you need blood tests to check drug levels, especially for warfarin, clobazam, or tacrolimus.
- Do not stop or change any prescription medication without talking to your prescriber first.
When to Call a Doctor
Seek medical help if you notice signs of a serious interaction. These include extreme sleepiness, confusion, trouble breathing, unusual bleeding or bruising, a racing or irregular heartbeat, or severe dizziness. If you feel unwell after using cannabis with other medications, contact your doctor or a poison control center.
Key Takeaways
- Medical cannabis can interact with many drugs, especially those metabolized by cytochrome P450 enzymes.
- CBD is a stronger enzyme inhibitor than THC.
- Blood thinners, anticonvulsants, opioids, and benzodiazepines are common concerns.
- Always tell your healthcare provider about cannabis use and never adjust prescriptions on your own.