This informal CPD article ‘A detailed look at how medical cannabis interacts with other medications’ was provided by Dr Sue Clenton, Medical Director and Specialist Consultant Oncologist at Releaf, a HealthTech company dedicated to transforming access to Cannabis Based Products for Medical use (CBPMs) in the UK.
With medical cannabis becoming more prescribed in modern healthcare, many patients are stopping to ask an important question: can medical cannabis be administered safely alongside other medications? (1, 2) The short answer is, it depends.
In many cases, patients can take prescribed cannabis-based medicines alongside other medications without experiencing any significant issues. (2) But, like with any type of prescription medicine (along with many over-the-counter treatment options), cannabis-based treatments can interact with other drugs and should always be monitored responsibly by a certified medical professional. (2)
Understanding the extent of these medical cannabis interactions requires improved awareness of two key areas: the conditions that medical cannabis is commonly prescribed to treat, and how cannabinoids act within the body. By developing a strong understanding of these areas, clinicians can help educate patients on the potential interactions that may occur when prescribing medical cannabis. This should then help support safer prescribing decisions, a more informed patient-provider dialogue and, ultimately, a better level of care.
Which conditions can medical cannabis be prescribed as a treatment for?
After the UK government changed the law back in November 2018, specialist doctors can now prescribe Cannabis-Based Medicinal Products (CBMPs) for conditions where they feel it is clinically appropriate. (1, 3) This includes a wide variety of conditions and symptoms, and is particularly recommended in cases where conventional treatments have failed to provide adequate relief or led to side effects. (1)
Some of the most common conditions associated with medical cannabis treatment include:
- Chronic pain
- Anxiety-related conditions
- Sleeping disorders
- Neurological conditions
- Gastrointestinal conditions
It’s also possible to be prescribed medical cannabis via the NHS, but this is much less common. (4, 5) The treatment is only prescribed for very specific conditions on the NHS, such as severe forms of epilepsy, adults with vomiting or nausea caused by chemotherapy or people with muscle stiffness and spasms due to multiple sclerosis. (4, 5)
Which medications may interact with medical cannabis?
While studies have listed 406 potential cannabis interactions, this does not necessarily mean medical cannabis should not be prescribed. (6) It simply demonstrates the importance of having a thorough understanding of each patient’s medical history.
By knowing which treatments are already being taken, clinicians can more easily identify any potential risks, adjust prescribing decisions where needed and monitor patients carefully to help ensure each treatment remains well tolerated. (2, 7)
Some of the main groups of medicines that may need closer consideration when prescribing medical cannabis alongside them include: (1, 2, 6)
- Anticoagulants or blood thinners
- Antiepileptic medicines
- Antidepressants and anti-anxiety medicines
- Anaesthetic agents or sedatives
- Opioid painkillers
- Immunosuppressants
- Certain heart medications
This does not mean that patients taking these medicines cannot be prescribed medical cannabis, but it does mean the prescribing clinician should review the combination carefully before deciding whether dose adjustments, additional monitoring or an alternative treatment approach is needed. (2)
How does medical cannabis interact with other medicines?
The liver is where most medication interactions take place, since it functions as the body’s primary site for drug metabolism. (8) When multiple substances are present in the body, they compete for the same metabolic pathways as one another, which can change how each one is metabolised. (8) This can lead to one substance being metabolised faster or slower than it normally would, potentially resulting in unexpected effects. (8, 9)
Liver enzyme system
How are THC and CBD metabolised?
Medical cannabis typically contains a specific ratio of tetrahydrocannabinol (THC) and cannabidiol (CBD). These are both metabolised in the liver by cytochrome P450 enzymes, where they are converted into different variations: (10, 11)
- THC converts into 11-OH-THC (a psychoactive metabolite) before being converted into 11-COOH-THC (its inactive form)
- CBD converts into 7-OH-CBD (a pharmacologically active metabolite, with no psychoactive effect) before being converted into 7-COOH-CBD (its inactive form)
Once these cannabinoids have been metabolised by the liver, both THC and CBD are primarily excreted via the faeces. (10, 11)
How shared metabolic pathways can affect other medicines
Because THC and CBD are metabolised through the same liver enzyme system as many other medications, they can interact with medicines that rely on the same metabolic pathways. (2, 8, 10, 11) CBD, for instance, is theorised to inhibit CYP450 enzymes such as CYP3A4 and CYP2C19. This means it can sometimes slow down how certain other medicines are metabolised by the liver, leading to increased levels within the body. (2, 10, 11)
This is why extra care may be needed when combined with medicines such as clobazam (an antiepileptic medicine), warfarin (an anticoagulant) or tacrolimus (an immunosuppressant), where even small changes in drug levels can be clinically significant. (2, 10) THC can also be affected by these shared pathways. For example, CYP2C9 and CYP3A4 are involved in THC metabolism, so medicines that inhibit or induce these enzymes may alter a patient’s THC exposure. (2, 10, 11)
The importance of this varies from patient to patient, which is why careful dose titration and regular monitoring are so important. It’s also important to note that these effects are not unique to medical cannabis. Many commonly prescribed medicines interact through the same metabolic pathways, so interactions are possible regardless of the type of medicine involved.
Not all drug interactions are due to how they are metabolised in the liver, either. (7) Some happen because two medicines have overlapping effects. Medical cannabis taken alongside medicines like opioids, benzodiazepines, sedatives or alcohol, for instance, may increase the likelihood of side effects like drowsiness, dizziness or cognitive impairment. (1, 2, 6)
Prescribing medical cannabis safely alongside other medicines
The key when prescribing medical cannabis alongside other types of medication is not to avoid treatment automatically, but to prescribe carefully. (2) This means taking the time to review each patient’s medical history, identify any possible interaction risks, monitor the patient regularly via follow-up appointments and adjust the dose where required.
The route of administration also matters. (1, 2) Research shows that oral oils and capsules can allow more controlled dosing, while inhaled products may work more quickly and require different safety considerations. (2)
Ultimately, medical cannabis can often be prescribed safely alongside other treatments, but only after clinicians have a detailed understanding of the patient’s medical history and the risk factors involved in their treatment. (2)
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References
- Medical Cannabis Clinicians Society. (2021). Recommendations and Guidance on Medical Cannabis under Prescription. [Internet]. Available at: https://www.ukmccs.org/wp-content/uploads/2025/12/Recommendations-and-Guidance-on-Medical-Cannabis-under-Prescription-3rd-Edition-2021-1.pdf
- MacCallum CA, Lo LA, Boivin M. "Is medical cannabis safe for my patients?" A practical review of cannabis safety considerations. Eur J Intern Med. 2021;89:10-18. https://linkinghub.elsevier.com/retrieve/pii/S0953-6205(21)00152-7
- GOV.UK. (2018) Rescheduling of cannabis-based products for medicinal use in humans (accessible version). [Internet]. Available at: https://www.gov.uk/government/publications/circular-0182018-rescheduling-of-cannabis-based-products-for-medicinal-use-in-humans/rescheduling-of-cannabis-based-products-for-medicinal-use-in-humans-accessible-version
- NHS. (2022). Medical cannabis (and cannabis oils). [Internet]. Available at: https://www.nhs.uk/medicines/medical-cannabis/
- NHS Inform. (2025). Medicinal cannabis. [Internet]. Available at: https://www.nhsinform.scot/tests-and-treatments/medicines-and-medical-aids/types-of-medicine/medicinal-cannabis/
- Drugs.com. (2026). Cannabis Interactions. [Internet]. Available at: https://www.drugs.com/drug-interactions/cannabis.html
- NHS Specialist Pharmacy Service, understanding drug interactions
- Susa ST, Hussain A, Preuss CV. Drug Metabolism. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2026. Available from: https://www.ncbi.nlm.nih.gov/books/NBK442023/
- Zhao M, Ma J, Li M, et al. Cytochrome P450 Enzymes and Drug Metabolism in Humans. Int J Mol Sci. 2021;22(23):12808. https://pmc.ncbi.nlm.nih.gov/articles/PMC8657965/
- Smith RT, Gruber SA. Contemplating cannabis? The complex relationship between cannabinoids and hepatic metabolism resulting in the potential for drug-drug interactions. Front Psychiatry. 2023;13:1055481. https://pmc.ncbi.nlm.nih.gov/articles/PMC9871609/
- MacDonald E, Adams A. The Use of Medical Cannabis with Other Medications: A Review of Safety and Guidelines - An Update. Ottawa (ON): Canadian Agency for Drugs and Technologies in Health; 2019. Available from: https://www.ncbi.nlm.nih.gov/books/NBK549545/
