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What Drugs Should Not be Taken With CBD?

If you're considering taking cannabidiol (CBD), understanding its compatibility with medications is essential.

This article aims to provide a comprehensive guide on the drugs that should not be taken with CBD. It will also shed light on the role of Cytochrome P450 enzymes in CBD metabolism and highlight the potential risks of combining CBD with certain medications.

By the end of this article, you will have a better understanding of the complexities of CBD and drug interactions, enabling you to make informed decisions about your health.

Introduction to CBD

Cannabidiol (CBD) is a naturally occurring compound derived from the cannabis plant. It has experienced a remarkable surge in popularity over the past years and become common in the practice of health and wellness worldwide.

The growing interest in CBD comes from a combination of factors, including a better understanding of its potential benefits and the availability of an expanding body of relevant scientific research.

Understanding CBD and its Uses

CBD is one of over a hundred cannabinoids found in the cannabis plant. However, unlike delta-9-tetrahydrocannabinol (THC), CBD does not produce a "high" or any intoxicating effects. This makes it an appealing option for those seeking the potential benefits of medical cannabis without the mind-altering effects or the risks associated with failing workplace drug tests.

CBD is most commonly sold as CBD oil, but it's also available in capsules, creams, and edibles. It's been studied for its potential role in easing symptoms of endocannabinoid deficiency and contributing to optimal health and a balanced endocannabinoid system.

However, it's crucial to remember that while CBD is a natural substance, this doesn't automatically make it safe in all circumstances. Like many other herbal supplements, CBD can interact with some medications.


The Role of Cytochrome P450 Enzymes in CBD Metabolism

To see why CBD should not be taken with certain substances and medications, it's crucial to understand how it's metabolised in the body. This metabolic process primarily involves a group of enzymes known as Cytochrome P450 (CYP450).

The CYP450 enzyme system, located mainly in the liver, is responsible for metabolising potentially toxic compounds, including over 60% of any drugs consumed. CBD, like many other substances, is extensively metabolised by this system. Specifically, the enzymes CYP2C19, CYP2C9, and CYP3A4 play significant roles in this process.

How CBD Interacts with Cytochrome P450 Enzymes

CBD's interaction with the CYP450 system is complex and multifaceted. Not only is CBD metabolised by these enzymes, but it also acts as a competitive inhibitor to them. This means that CBD can occupy the site of enzymatic activity, displacing other chemical competitors and preventing the CYP450 system from metabolising other compounds. By inhibiting these enzymes, CBD can affect how other medications are metabolised, potentially causing their increased concentration or reducing their effect.

Moreover, CBD's interaction with the CYP450 system can be influenced by various factors, including the dosage of CBD, the presence of other medicines, and individual genetic variations in CYP450 enzymes. For instance, the CYP2C19 enzyme can be present in different forms, leading to differences in how CBD and other substances are metabolised.


Specific Drugs that Should Not Be Taken with CBD

Research has identified several classes of drugs that should not be taken with CBD due to potential adverse interactions. These include:

  • antiepileptic drugs - clobazam, stiripentol, and valproate
  • anticonvulsants - diazepam, lamotrigine, and phenytoin
  • sedatives - phenobarbital, hexobarbital30, codeine and morphine
  • antidepressants - omeprazole risperidone, tranylcypromine, phenelzine, and isocarboxazid
  • benzodiazepines - chlordiazepoxide, clonazepam and ethosuximide
  • thyroid medication - levothyroxine

Each drug class is followed by specific examples of drugs that have been found to interact with CBD in a comprehensive 2021 review by Balachandran, Elsohly and Hill.

Not all interactions will produce the same results. For instance, CBD's interaction with antiepileptic drugs such as diazepam, lamotrigine, and phenytoin can lead to increased drug concentration, potentially exacerbating side effects. However, its effect on chlordiazepoxide, clonazepam and ethosuximide (benzodiazepines) is to reduce their anticonvulsant effects.

Therefore, individuals taking these medications should exercise caution when considering CBD use and consult with a healthcare professional before starting any CBD regimen.

Important note- Any lists of medications or classes of medications in this article are not exhaustive. The UK Food Standard Agency (FSA) recommends that anyone taking medication should not use CBD unless under medical direction.

The Grapefruit Warning: A Key Indicator for Potential CBD Interactions

A simple rule of thumb for identifying potential CBD-drug interactions is the "grapefruit warning." Many medications come with a warning against consuming grapefruit, as this fruit can inhibit the same set of liver enzymes as CBD, leading to various effects, including increased drug concentration.

If your medication comes with a grapefruit warning, it's likely that it may also interact with CBD. However, this is a general guideline, and individual responses can vary.

Case Studies of Adverse Effects from CBD and Drug Interactions

As the use of CBD continues to rise, so does the need for a comprehensive understanding of its potential interactions with other substances. While research is ongoing, several case studies have highlighted the adverse effects that can occur when CBD interacts with certain medications.

These real-life instances provide valuable insights into the complexities of CBD and drug interactions, underscoring the importance of medical consultation before incorporating CBD into a wellness routine.

Real-life Instances of Negative CBD and Drug Interactions

One notable case involved a patient taking 7.5 mg of warfarin, a common blood thinner, daily alongside CBD. He was placed on the starting dose of CBD at 5 mg/kg/day divided into two equal parts and taken twice a day. This was increased in 5 mg/kg/day increments every two weeks. The interaction between CBD and warfarin led to an increased risk of bleeding, necessitating a 30% reduction in the patient's warfarin dose.

In another instance, a patient combining CBD with the antiepileptic drug valproic acid experienced abnormally high liver enzyme levels, indicating potential liver problems. This case underscores the need for careful monitoring of liver health in patients using CBD alongside certain antiepileptic drugs.


These case studies highlight the potential risks associated with combining CBD with certain medications. They underscore the importance of consulting with a healthcare provider before starting CBD, particularly for individuals already taking prescription meds.

Healthcare providers can provide personalised advice based on a patient's specific health conditions and current medications, helping to minimise the risk of adverse CBD-drug interactions. They can also monitor patients for potential side effects, enabling timely intervention if necessary.

The Role of Pharmacists in Preventing Adverse CBD-Drug Interactions

Pharmacists play a crucial role in preventing adverse CBD-drug interactions. With their extensive knowledge of drug metabolism and interactions, some pharmacists can provide valuable advice on safe CBD use. They can identify potential interactions based on a patient's current medications, advise on appropriate CBD dosages, and monitor patients for potential side effects. Therefore, some doctors may recommend consulting with a pharmacist before starting any CBD regimen.

The Importance of Ongoing Research

While these case studies provide valuable insights, more research is needed to fully understand the complexities of CBD and drug interactions. Ongoing research can help identify additional drugs that may interact with CBD, clarify the mechanisms underlying these interactions, and develop strategies to prevent adverse effects. As our understanding of CBD continues to evolve, this will enable us to harness its potential benefits while minimising its risks.

The Importance of Medical Consultation Before Using CBD

It's crucial to understand that while CBD offers various potential benefits, it's not without risks. One of these risks is the potential for interactions with other medicines. This is why the FSA advises against the use of CBD for anyone on medication unless directed by a doctor.

Why You Should Always Consult a Healthcare Professional

For anyone on medication, a specialist medical practitioner should play a pivotal role in ensuring the safe and effective use of CBD. They have the knowledge and expertise to assess your overall health status, consider your current medications, and determine whether CBD is a suitable option for you. They can also guide you on the appropriate dosage of CBD to minimise the risk of adverse effects.

Moreover, specialist healthcare professionals are equipped to monitor your response to CBD over time and make necessary adjustments to your treatment plan.

This is important for individuals with chronic conditions (for example, chronic pain, chronic kidney disease, weakened immune system, and chronic central nervous system diseases) or those taking prescription medication, particularly if you're wondering if your medication can be taken with CBD.


The Importance of Informed Decision-Making in CBD Use

Informed decision-making is key when considering CBD use. This involves understanding the potential benefits and risks of CBD, including its potential interactions with other medications. It also involves seeking professional medical advice and adhering to recommended dosages and guidelines for safe use.

Understanding the Potential Risks and Benefits of CBD

Before starting any CBD regimen, it's important to understand both its potential benefits and risks. On one hand, CBD is a 100% natural supplement that doesn't produce any intoxicating effects. It also promotes the health of the body's endocannabinoid system, allowing your body to maintain a state of healthy balance.

However, on the other hand, studies have found that for some people, it produces side effects. It also interacts with several medications, interfering with their potency and effects.

Therefore, it's crucial to get specific about why you want to take CBD, how it might affect the medication you're using and what results you hope to get from using it.

Adherence to recommended dosages and guidelines is crucial for safe CBD use. This includes following the information provided on the label of CBD supplements, the advice of healthcare professionals, and the consumer guidelines provided by the FSA. It's also important to inform your healthcare provider about any changes in your health or medications, as these may require adjustments to your CBD regimen.


When considering the question, 'What drugs should not be taken with CBD?' it's important to remember that the intricacies of our biological systems influence the complex interaction between CBD and different medications.

CBD, like grapefruit, interacts extensively with the cytochrome P450 enzyme system. P450 enzymes play a crucial role in metabolising many prescription drugs (CBD is not the only substance that does this). CBD can inhibit the function of CYP450 enzymes, leading to drug interactions, potentially causing adverse effects or reducing the efficacy of certain medications, including antiepileptic drugs, antidepressants, benzodiazepines, opioid analgesics, and blood thinners.

The Future of CBD and Drug Interaction Research

Looking ahead, more research is needed to fully understand the extent of CBD's interactions with various prescription medications. Studies have shown that both CYP2C19 and CYP2C9 enzymes play significant roles in CBD metabolism, but the full implications of these interactions remain to be explored.

Furthermore, the different possible structures of CYP2C19 suggest that individual genetic differences may lead to variability in how different people metabolise CBD. This area of research could provide valuable insights into personalised medicine approaches to CBD use.

On the whole, while CBD holds promise for various applications, its potential interactions with other medicines necessitate caution. Always consult with a healthcare professional before starting any new treatment regimen, including CBD, especially if you're already taking other medications. As research progresses, we can look forward to a deeper understanding of CBD (both supplements and prescription CBD) and its place in modern medicine.