CBD | Science

CBD & Drug Interactions: The Science

As interest around CBD improved, questions around CBD drug interactions naturally increases. 

Many drugs, when taken together, or within a short period of each other, have the potential to interact. Cannabidiol (CBD), although a naturally occurring compound, still becomes a drug as soon as it enters the body. 

When we talk about drugs working with each other in the body, we mean when the intended effects or side effects are altered by the simultaneous ingestion of another substance (a food, supplement or beverage can also cause this).

This change is often unwanted and, in some cases, dangerous, but it can also be positive – when a drug interaction is considered positive, it is commonly referred to as synergistic. For example, you may notice some paracetamol containing flu remedies also contain caffeine; this is because caffeine increases the effects and absorption of paracetamol. 

CBD pharmacy drug interactions discussion

Types of Interactions

There are two different classifications of drug interactions – pharmacokinetic and pharmacodynamic. 

Pharmacokinetic interactions refer to how one substance affects the rate in which another is absorbed and transported around the body. Additionally, it may also affect the rate at which the drug is metabolised and excreted. This type of interaction will result in varying levels of the drug in your body.

Pharmacodynamics relates to the effect of a drug on the body: Two drugs may have similar effects, and when taken together, may heighten or lessen the intended impact of one another.

For example, two drugs that cause sedation when taken together may result in an increased sedative effect. Conversely, one may counteract the effect of another, like taking one drug to increase your blood pressure while taking another that may reduce it.

Early Research

Currently, there is very little tangible evidence referring to CBD drug interactions due to the limited number of clinical studies. On the flip side, several small studies have looked into how CBD is thought to metabolise in the body.  So what drugs should not be taken with CBD?

One study looked into interactions between CBD and commonly used antiepileptic drugs, resulting in raised levels of these drugs in the body. Also finding elevated Liver Function Test markers (LFT), which in some cases can represent toxicity or potential damage.

Clobazam is another drug that is used to treat epilepsy and in some cases, anxiety. A small study of 13 children investigated the use of CBD and clobazam in children, revealed that after four weeks of treatment clobazam levels rose significantly, resulting in increased side effects such as drowsiness, ataxia and irritability. On the more positive side, the study revealed a 50% decrease in seizures amongst 9 (69%) of the patients.

The use of CBD in epilepsy is one of the most documented use cases of cannabidiol. In the US, the FDA approved the medicine Epidiolex in 2018, a highly concentrated form of CBD for use in treatment-resistant epilepsy such as Lennox-Gastaut syndrome or Dravet syndrome. 

Closer to home, GW Pharma recently received a positive recommendation from the European Medicines Agency to license Epidiolex in the EU for the same two conditions for children aged 2 and over.

There is a limited amount of research that has looked into the effects of CBD and anticoagulants/antiplatelets (drugs that ‘thin’ your blood to reduce blood clotting), commonly prescribed medicines in this class include aspirin, clopidogrel, warfarin, and apixaban. Studies indicate that CBD can have similar effects to these drugs, therefore increasing the likelihood of bleeding. 

pharmacy bottles on shelf cbd

What drugs should not be taken with CBD?

When a drug is consumed, it is usually metabolised by the liver or kidneys. 

Data from both pre-clinical and human studies suggest that CBD is metabolized by the liver, by a group of enzymes that metabolize many other drugs, cytochrome P-450 isoenzymes, specifically CYP2Cs and CYP3A4 (CYP3A4 metabolizes approximately 60% of clinically prescribed medications).  

If you consume medication with a warning not to eat or drink grapefruit juice while taking this medication, there is an increased likelihood of a drug interaction.

Studies in mice suggest CBD can inhibit cytochrome P450 enzymes initially, in the short term, but can then induce them after repeated dosing. Vitro studies (studies that are performed outside the human environment) indicate CBD to be a potent inhibitor of CYP3A4 and when an individual uses a medication that is metabolized through this enzyme, there is a potential for conflict. 

It should also be noted that this can work the other way around; drugs may have the potential to increase and decrease the levels of CBD in your body when taken together. 

Research indicates certain drugs such as ketoconazole, itraconazole, ritonavir, and clarithromycin inhibit CYP3A4, and lead to a slower metabolism of CBD and therefore increase the level of the substance in the body. 

Conversely, research also outlines the potential for the opposite effect for phenobarbital, rifampicin, carbamazepine, and phenytoin, which induce CYP3A4, leading to increased metabolism and subsequent lower levels of CBD in the body.


It’s clear there are several potential drug interactions with CBD. 

The current evidence is limited and pre clinical evidence doesn’t always correspond to the same result in human studies. More work needs to be done to fully identify the positive and negative possibilities, along with the potential risks of taking CBD with other drugs.

Always consult with your doctor before adding new supplements like CBD to your diet, only your physician can give you medical advice.