EducationWhat drugs should not be taken with CBD?

What drugs should not be taken with CBD?

8 min read

Lucy MacKinnon

What drugs should not be taken with CBD?


Drug interactions can be extremely unpleasant, but unfortunately, they are an all too common occurrence within the medical world. With around 13% of Brits using CBD products to manage a range of conditions, here at Releaf we feel it is important to explain the risks of taking CBD alongside other drugs or medications.

CBD, or cannabidiol, is a chemical compound found within the cannabis plant family that has been used as an ingredient in alternative, holistic, and traditional medicines for millennia. 

With a host of reported potential therapeutic benefits and a lack of intoxicating effects or serious adverse reactions, the cards really are stacked in cannabidiols' favour, and so CBD’s rising popularity should come as no surprise.

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 other drugs

Scientists have discovered 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 majorly 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 metabolisation speed of other drugs 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.

Another important substance to mention is 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. Scientists believe this reduces the intensity and likelihood of experiencing the intoxicating or euphoric effects that are commonly associated with this cannabis compound.

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 attribute 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 all consumed together.

What drugs should not be taken 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 doses. 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.

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. Pain killers, and certain medications that are designed to lower cholesterol, have also been associated with liver damage. 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.

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.


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.

Although CBD is generally deemed safe, complications can arise when it is consumed alongside other drugs, substances or prescribed medications. As previously mentioned, your doctor 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.

It is important to seek medical advice before starting any new treatments. The patient advisors at Releaf are available to provide expert advice and support. Alternatively, click here to book a consultation with one of our specialist doctors.

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With five years of journalism and healthcare content creation under her belt, Lucy strives to improve medical cannabis awareness and access in the UK by producing high quality, credible content.

Our articles are written by experts and reviewed by medical professionals or compliance specialists. Adhering to stringent sourcing guidelines, we reference peer-reviewed studies and scholarly research. View our editorial policy.

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