Cannabis and Prescription Medicine Known Interactions

The road map for patients with long lists of prescription medications and an opportunity to take cannabis (THC/CBD) as an additional medication can be hard to navigate. Many providers are undereducated in this area, and the best tools available to them are not complete regarding drug to drug interaction. Let me start by sharing the basics of what is available.  

There are three pharmaceutical products available (not all in US) that mimic/contain THC and/or CBD:

1. Marinol (Dronabinol) is a prescription drug available in the US used to treat nausea and vomiting caused by cancer chemotherapy. It is also used to treat loss of appetite and weight loss in cancer and HIV patients. Dronabinol is a synthetic man-made substance that mimics THC.

2. Epidiolex is a plant-derived cannabidiol (CBD) product approved in 2018 by the FDA as a prescription to treat seizures in patients with difficult to treat childhood onset epilepsy.

3. Sativex (Nabiximols) is an oromucosal spray formulated as an extract of the cannabis plant that contains a 1:1 ratio of CBD:THC. It is available in 25 countries outside of the US to treat muscle stiffness and spasm due to Multiple Sclerosis, but not in the US.

Having these products on the market made way for a listing in the PDR/drug interaction checkers for providers and pharmacists. With this, we know some basics about areas to watch related to medical cannabis use and drug interaction. Potential interactions of cannabis (THC and CBD) based on the above noted medications on the drug interaction checker:

1. Blood thinners, but specifically, Coumadin, should be monitored closely. This is not to say it cannot be used, but blood levels with use should be monitored because they compete to be bound to a protein and could lead to prolonged and increased amounts of either medication in the blood. Simply stated, PT/INR levels that are checked routinely when on Coumadin might change causing a prescribed dose to change and/or blood being thinner than desired. Taken further, if the patient were to haphazardly discontinue cannabis therapy and not closely monitor PT/INR with lowered amount of Coumadin, blood would be at risk for more coagulation.

2. Sedatives/Narcotics (medications that may cause drowsiness or central nervous system depression) are not considered drug interactions; however, patients should go low and slow when adding cannabis to prevent additional drowsiness/sedation when used in conjunction with these types of medications. For example, if a patient takes a sleeping pill nightly that knocks them out, and then they add a high dose of a sedating cannabis option for sleep, they are likely to have an increased sedative effect.  

Bottom line, there are no documented “hard stop” drug interactions between the pharmaceutical and the plant-derived cannabinoids. As with any new medication or natural supplement, patients should communicate with each of their providers, and go low and slow while monitoring the effect of the new addition to their medication regimen. Having a plant-based, integrative medicine type nurse coach can be useful as well. 🙂 Ask for Nurse Laura at