CBD Drug Interactions Explained: What Drugs Should Not Be Taken With CBD

Cannabidiol, or CBD, is one of over a 100 different types of a specific kind of compound called phytocannabinoids found in the Cannabis sativa plant.

CBD is has become increasingly popular in recent years due to its wide range of therapeutic effects as well as its ability to relieve a host of symptoms effectively , but also to do so safely and with few side effects. And unlike tetrahydrocannabinol (THC), the other most abundant phytocannabinoid found in the cannabis plant, CBD is non-intoxicating and non-psychoactive - something that for many people is an undesirable yet unavoidable part of taking a high-THC containing cannabis extract.

CBD is most widely known and has been popularized as being used for seizure disorders such as epilepsy but has also proven to be effective in helping to relieve the symptoms of other conditions. These include anxiety, depression, schizophrenia, inflammatory and neuropathic pain, Parkinson's disease, Crohn’s and other forms of inflammatory bowel disease, as well as certain types of cancer.

However, despite the fact that the vast majority of the science indicates CBD oil is safe to use on its own, CBD is a powerful compound that interacts with a variety of systems within the body. And as such, CBD not only shows potential as a powerful therapeutic agent, but can become less benign when taken together with other substances such as pharmaceutical drugs.

Let’s find out why.

Understanding Metabolism

Before we take a look at how CBD interacts with medications, first we need to understand how the body’s metabolism works in general, the systems involved in CBD metabolism, how CBD is metabolized and how CBD affects something called the Cytochrome P-450 system.

What Is Metabolism?

A lot of people think of metabolism in terms of how easily or slowly they gain and lose weight, often claiming to have a “fast” or “slow” metabolism. In scientific terms, this is what is known as the basal metabolic rate, or the amount of calories an individual requires in order to sustain normal body functions while at rest.

However, this basal metabolic rate is very different to metabolism - the way in which substances such as different types of food are broken down and used by the body - with much of this process happening in the gut and the liver in what is known as the ‘first-pass effect,’ or ‘first-pass metabolism’.

Explained very simplistically, when food is eaten, it is broken down by the liver into its individual compounds in order for it to be used by the body. So for example, carbohydrates are broken down into sugars, fats into triglycerides, and proteins into amino acids. From there, the metabolism, under the control of chemicals called enzymes, transforms these compounds into metabolites that can then be used by the body, for instance as fuel for cellular processes or as building blocks for various systems and tissues.

Just like food has to go through this process, so too does a therapeutic compound such as CBD, but in what is more specifically called drug metabolism. Drug metabolism refers to the rate at which medications and other therapeutic compounds are broken down by the body into its individual metabolites and how long these metabolites stay in the body.

So, when CBD is ingested by mouth, either as an oil, tincture, capsule or edible, it has to pass through the digestive system where the it is absorbed into the bloodstream by the intestines. From there, the CBD is transported by the blood to the liver where it enters the liver via the hepatic portal. Once the CBD is in the liver, it is broken down into its metabolites by enzymes after which it can be circulated throughout the body in the bloodstream.

The Cytochrome P450 System

However, in addition to breaking compounds down into metabolites, is also has one other very specific and important role it plays during this metabolic process - the detoxification and excretion of foreign drugs (called xenobiotics) and other types of toxic substances.

It does through a system called the cytochrome P450 system (CYP) which consists of a special group of enzymes containing heme as a cofactor to convert fat-soluble compounds into more water-soluble compounds and aiding in their absorption and use.

It is estimated that the CYP system is responsible for metabolizing over 60% percent of any drug that has been consumed. And interestingly, pharmaceutical researchers and doctors also use cytochrome P450 system to understand, calculate and predict drug dosages, effects as well as its potential side effects.

For instance, if only one therapeutic compound is being processed by the liver, and the system in general is healthy, scientist can use the average amount of time it takes for the drug or medication to be processed through the CYP to calculate accurate dosage information.

However, there are certain substances that have the ability to affect the way in which the CYP system processes compounds such as CBD that causes certain drugs to metabolize faster or slower than what they would normally have done.

CBD And The Cytochrome P450 System

As mentioned, CBD also has the ability to interact directly with the CYP system in the liver. Preclinical research is showing that the way in which CBD does is by binding to the site where the enzyme activity occurs acting as a “competitive inhibitor”, displacing its chemical competitors, and thus preventing the CYP system from metabolizing other compounds.

The extent to which CBD acts as a competitive inhibitor of the cytochrome P450 binding proteins is mainly dependent on how much CBD is ingested, the unique physiology of the individual as well as the type of CBD product used (e.g. CBD isolate v.s full-spectrum CBD extracts). This is due to these factors determining how tightly the CBD molecules bind to the active site of the metabolic enzyme, with increased and tighter bonds resulting in more competitive inhibition.

What this means in plain English is that CBD sort of “out competes” other medications when it comes to reaching first place in for getting metabolized by the CYP enzymes. This, in essence means that CBD deactivates the effects of all the other therapeutic compounds that pass through the CYP system.

How successful it is in its competition with other medicines depends on a few factors but mostly the amount of CBD that enters into the bloodstream. If it’s not very much, it will have very little to no noticeable effect on the CYP activity and the majority of the medicine will be metabolized. On the other hand, if a large dose of CBD is taken, it will bind to a lot more of the site of enzyme activity and leave a lot more of the other medicine to not be metabolized.

Why CBD’s Competitive Inhibitory Effect On The Cytochrome P450 System Is Important

When the CYP system is affected in this way by CBD, it both changes and the way in which certain other drugs are metabolized as well as prevent a lot of the drug to be metabolized. When this happens, it leads to higher levels of other drug compounds to remain in the body at a single time.

At the very least these elevated concentrations can cause unwanted side effects like an increased risk of bleeding or a suppressed immune system, but more worryingly, it can quite easily result in an overdose.

CBD and Drug Interactions: Contraindications

Any therapeutic compound that is metabolized by the CYP system has the potential of being affected by CBD. One indication that your medicine might be metabolized by the CYP system is if your pharmacist told you not to eat grapefruit or watercress or use St. John’s Wort or goldenseal supplements. However this is by no means a solid test and you should always check with your pharmacist of doctor first (more on that later).

According to the Indiana University Department of Medicine, pharmaceutical drugs and medications which could be contraindicated for use with CBD include: