What drugs should not be taken with CBD?

Why interactions with other medications matter

Although generally deemed as medically safe when taken alone, CBD has been known to increase the side effects of other prescribed medications or alter their efficacy. This article will discuss how drugs interact with CBD, what drugs should not be taken with CBD, and what precautions to take when using cannabidiol alongside other drugs or medications.

But, before we venture forth, it is critical to state that you must always seek professional medical advice before making any changes to your current treatment plan. Medicinal cannabis can only be prescribed by specialist doctors who will have a full and proper understanding of the interactions that CBD can have with other prescription medications.  

How CBD interacts with your body: metabolism and enzyme pathways

Scientists have found that, much like many other forms of medications or therapeutic products, CBD is broken down by a family of proteins in the human liver called Cytochrome P450 Enzymes (CYP). 

Enzymes like CYP3A4 and CYP2D6 metabolise (break down) drugs and substances in the liver, allowing them access to the bloodstream and the ability to travel throughout the body in their ‘active’ forms, causing reactions within the body. However, when certain medications are administered alongside CBD, the productivity of CYP enzymes can be significantly affected.

If dosages have not been calculated by a doctor, when taken together there is a chance that CBD may interfere with the metabolism, efficacy, and the effects of other medications. 

In some cases, CBD can slow down the speed at which other drugs are metabolised by hindering certain enzymes, which can lead to increased side effects. Alternatively, CBD has also been shown to speed up the metabolism of other medications, which reduces their efficacy window – something that is not typically rectified until the dosage is corrected.

Medications can interact with CBD

Compared to many other conventional medications, there are very few CBD side effects that are considered to be dangerous or severe, and in 2017 the World Health Organisation deemed cannabidiol “does not appear to have abuse potential, or cause harm”. 

However, when taken alongside another medication or supplement that can have similar effects, the probability of experiencing adverse drug reactions is effectively doubled. This is relevant in the case of ‘safe’ side effects, like fatigue or drowsiness, and more serious side effects, like an increased risk of liver damage.

One of the more common, and minor, side effects associated with CBD is increased fatigue or drowsiness. This can also be seen in the case of common antihistamines, opioids, and tricyclic antidepressants. If CBD is taken with these drugs, there is an increased likelihood of fatigue or increased sleepiness, which can lead to unfortunate accidents. 

For this reason, it is important to take precautions when deciding on CBD oil dosage (or any other CBD product dosage size. You should always seek the professional advice of specialist doctors registered to prescribe CBD and other medicinal cannabis products to avoid potential side effects like this.

Serious drug interactions with CBD to watch out for

In 2019, an animal study involving mice uncovered a possible link between CBD and liver damage, adding liver toxicity to CBD’s list of potential side effects. Epidyolex was used in this experiment, a form of medication that is currently approved for use in the treatment of rare forms of epilepsy in the UK. 

In this study, the subjects tolerated Epidylox well, but they did show signs of increased liver toxicity, which can be dangerous and should be monitored by a healthcare professional. Painkillers and certain medications that are designed to lower cholesterol have also been associated with liver damage.

The following year, a large-scale investigation of existing data by researchers at Penn State College of Medicine in Pennsylvania found that cannabis cannabinoids have the potential to dangerously affect 57 different types of medications. Much of these severe interactions occur as the concentrations of medications are altered by a combination of CBD and THC, however, these interactions are also possible when cannabinoids are applied individually.

In the case of CBD specifically - common blood thinners, thyroid medications, and seizure medications have all shown to have potentially serious interactions with CBD and so, they should not be taken with cannabidiol. This is also the case with some heart rhythm medications.

This only acts to highlight just how imperative it is to inform your doctor of any CBD administration if you are currently taking these prescribed medications.

CBD and alcohol: Is it safe to take CBD if you drink alcohol? 

In a health survey conducted by Forbes in 2022, it was found 64% of 2,000 US adults believed CBD was safer for humans than alcohol, but this survey failed to establish whether respondents were aware of any risks when consuming CBD alongside alcohol. 

Forbes later followed this up in an article explaining that there is limited research on the possible interactions between alcohol and cannabidiol, but they interviewed Chief Nursing Officer Eloise Theisen about the subject.

Eloise Theisen explained:

“If someone took CBD in the morning to help with their anxiety and wanted to have a drink or two in the evening, that [combination] hasn’t shown to be problematic.

Taking them concurrently is where I get concerned because of the potential side effects - whether from the alcohol or even the CBD.”

How CBD interacts with THC

CBD is also known to interact in contrasting ways with its phytocannabinoid cousin: THC. 

Instead of interacting with the metabolism of THC, cannabidiol is able to negatively affect tetrahydrocannabinol’s binding affinity to CB1 receptors (CB1) in the human brain. By altering the shape of CB1 receptors in the endocannabinoid system, it is said CBD weakens the effects THC is able to have on the brain. 

Researchers believe this reduces the intensity and likelihood of experiencing the intoxicating or euphoric effects that are commonly associated with this cannabis compound.

The entourage effect explained

Other evidence suggests that CBD also interacts with other cannabinoids, terpenes and flavonoids in a synergistic manner, producing a more rounded set of effects on the patient than when CBD is administered in isolation. This theory, coined the 'entourage effect', has been widely accepted amongst the medical and wellness industries due to its appearance in multiple trials.

A 2010 double-blind, randomised, placebo-controlled study analysed the difference in effects, tolerability, and safety of a THC extract and a balanced THC:CBD extract in the possible treatment of intractable cancer-related pain. The most significant improvement in pain levels was reported by participants in the whole plant group, who received the balanced THC:CBD extract. 

Another pain study from 2014 displayed potentially more effective results when using full-spectrum cannabis extract - this time a combination of THC and CBD was concluded to be more effective in the treatment of pain than a highly purified CBD extract. 

Both of these studies contribute to the entourage effect’s mounting evidence, suggesting CBD interacts with other cannabis compounds like THC, different terpenes, and flavonoids to create a more beneficial effect on its patients when they are taken together.

Is CBD dangerous when taken with other drugs?

Now we are getting to the real question - is CBD a dangerous addition to certain treatment plans? 

The World Health Organisation states:

“CBD is generally well tolerated with a good safety profile. Reported adverse effects may be a result of drug-drug interactions between CBD and patients’ existing medications. Several countries have modified their national controls to accommodate CBD as a medicinal product. To date, there is no evidence of recreational use of CBD or any public health-related problems associated with the use of pure CBD”

So, while CBD is seen to be relatively safe when taken on its own, it can complicate things when paired with other medications.

Because CBD alters the way the body processes certain drugs (mainly through its effect on liver enzymes like CYP3A4 and CYP2D6) it can either slow down or speed up how quickly other medications are metabolised.

This means that, in some cases, the levels of another drug could become too high, leading to stronger or unexpected side effects. In other cases, the opposite could happen: the medication could be cleared from the body too quickly, reducing its intended effect.

Neither scenario is ideal. And this is why it is absolutely essential to speak to a clinician if you are considering CBD while already taking prescription medication.

In particular, people taking blood thinners, seizure medications, thyroid treatments, heart rhythm drugs, or anything that relies on a precise dosage to be effective should be especially cautious. 

What should you do if you take other medications and want to use CBD?

First things first - reach out to a specialist who has experience in prescribing medical cannabis, especially one that does so for your specific health condition. 

Here at Releaf, we have a world-class clinical team, with experience supporting patients across a wide range of conditions - from chronic pain, mental health, and sleep issues to autoimmune and neurological disorders.

Our specialists and support staff understand the complexities of CBD interactions and can guide you through the safest options based on your individual health profile.

Before starting any CBD product, it is important to review your full list of medications, consider any potential drug interactions, and create a plan that monitors both safety and effectiveness over time. That is exactly what we offer to every single Releaf patient. 

Check out How long does CBD take to work, and how long does it stay in your system? for more information. 

Final thoughts: what you need to know about CBD and medication safety

With 40% of European CBD users consuming cannabidiol-based products more than once a week, we feel it is important that every patient understands the probability and possibility of dangerous side effects. 

By taking the necessary precautions advised in this article when using other drugs and substances in combination with CBD, you will drastically lower any chances of these negative interactions occurring. Your medical cannabis prescribing specialist will be able to advise you specifically on what medications should not be taken with CBD to avoid serious side effects.

Don't let the stigma surrounding medical cannabis prevent you from getting a suitable treatment. Releaf provides tailored monthly packages, specialist consultations for medical cannabis, and a unique medical cannabis card for protection, all based on your medical cannabis prescription.

To find out if you're potentially eligible for a legal UK medical cannabis prescription, pop over to our medical cannabis eligibility checker. It takes less than 20 seconds to complete, and could be the first step toward safer, more personalised treatment.