Medical cannabis for cancer-related treatment side effects and secondary symptoms: assessing the current evidence

This informal CPD article ‘Medical cannabis for cancer-related treatment side effects and secondary symptoms: assessing the current evidence’ 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.

For many oncologists, medical cannabis is a topic being widely discussed by more and more patients. (1) Many are keen to understand how taking it as an adjunctive medication may help to alleviate certain cancer-related symptoms and side effects brought on by chemotherapy and other related treatments. 

This thirst for understanding is nothing new and actually tallies with the American Society of Clinical Oncology (ASCO) guidelines from a few years back. (2) Back in 2024, ASCO published guidance on cannabis and cancer, which said that access and use among adults with cancer had, in its own words, “outpaced the science supporting its clinical use”. (2)  While this guidance is American-focused, it can leave UK clinicians in a slightly tricky spot. Most clinicians want to be able to give clear, honest guidance based on the relevant UK regulatory standards. However, in many areas, the research is still catching up, and patients are becoming more tuned in than ever before, especially to updates from further afield in other countries. 

It is therefore worth considering two key questions. First, what do we actually know about medical cannabis for cancer-related side effects and secondary symptoms? And second, how can clinicians guide UK-based patients to understand the potential benefits and drawbacks based on the latest clinical evidence?

Why are more cancer patients asking about medical cannabis?

Many cancer patients are interested in medical cannabis for one main reason: to help with the symptoms and side effects that cancer treatments can cause. While medical cannabis cannot cure or target the cancer itself in any way, the cannabinoids it contains may help certain eligible patients to manage secondary symptoms of the condition, including nausea and pain. (3) It may help to improve certain lifestyle issues that often appear when living with cancer as well, such as sleep-related disturbances, lack of appetite or mental health problems like anxiety or low mood. (3)

There are also the actual side effects of the cancer treatments to consider as well. Conventional cancer treatments like chemotherapy may be highly effective at targeting cancer cells, but they are also associated with several debilitating side effects, like vomiting, nausea, sleep-related issues, and chronic pain. (4) Medical cannabis cannot offer a cure for these issues. But it may help to ease the day-to-day burden of living with cancer and the overall treatment process. 

What does the evidence say about medical cannabis for cancer-related symptoms and side effects? 

Considering medical cannabis as a method to treat cancer symptoms and the side effects of certain conventional pharmaceutical interventions is almost always about offering supportive care to patients, rather than as a first-line treatment. In other words, it’s about easing associated symptoms and helping to manage side effects, which is where most of the latest clinical research has focused. 

With this in mind, the following are some of the main areas patients ask about, and highlights what the evidence has found so far:

• Nausea and vomiting: This is the symptom medical cannabis is most commonly associated with in terms of cancer. In fact, there are already licensed synthetic cannabinoid-based medications available in the UK, which can be offered to patients when other forms of antiemetics haven’t worked. (5) Recent trials into THC: CBD capsules have also shown reduced levels of nausea and vomiting when compared to a placebo, so the research is much stronger in this area. (6)
• Cancer-related pain: The evidence in this area is a little more mixed. Some studies have found that medical cannabis can safely relieve cancer pain and reduce patient reliance on opioids and other pain-relief medications. (7) However, further research is needed to fully understand the relationship.
• Sleep-related disturbances: The pain associated with cancer can make sleep not only challenging to come by, but also make it difficult to stay asleep when it does. However, medical cannabis has been shown in some studies to help manage these sleep disturbances (8), with an analysis from the UK Medical Cannabis Registry also reporting significant improvements in sleep quality among patients who had a prescription. (9)
• Lack of appetite: Figures show that 50% of people diagnosed with cancer are estimated to experience loss of appetite, rising to 60% in advanced forms of cancer. (10) Medical cannabis may be able to alleviate this issue by stimulating hunger through how it interacts with the body’s endocannabinoid system. (11) But further research is needed. 
• Anxiety, depression and low mood: Mental health-related issues can appear at any stage of the cancer treatment pathway and make everyday life more difficult to enjoy. Medical cannabis has been shown, again by the UK Medical Cannabis Registry, to help with these issues, improving overall quality of life and overall feelings of anxiety. (12) In cancer patients specifically, products higher in CBD have also been found to be more effective at relieving these issues than THC. (13) However, further research involving more patients and bigger trials is needed.

These results show a lot of promise, but it’s important to note that the majority of clinical evidence in this area is of a low or very low level of certainty, as highlighted in ASCO’s 2024 review. (2)

That said, some cancer patients have reported to clinicians a noticeably positive impact from taking medical cannabis as an adjunctive treatment, something which has been mirrored by numerous patient surveys. (14, 15) As such, offering a tailored approach to patients with cancer is crucial. 

Looking at the bigger picture: potential confusion, issues and things to watch out for

As promising as medical cannabis can be to some eligible patients, there are a few practical considerations that are important to be aware of, as well as some common questions clinicians are often asked. Providing false or misleading information in this situation can unintentionally lead to increasing the stigma surrounding medical cannabis in cancer (16) and lead to potential confusion among patients. 

So, here are a few of the main areas that are worth paying particularly close attention to when managing the patient-provider relationship. 

NHS availability

Medical cannabis can only be prescribed for three health concerns on the NHS: two rare forms of childhood epilepsy, MS spasticity, and chemotherapy-induced sickness. (17) As such, patients will likely need to consult a specialist at a private clinic to determine their eligibility. 

Interactions with other cancer treatments

The cannabinoids that medical cannabis contains, namely THC and CBD, can both affect how other forms of medication work in the body. So, it’s important to consider the full treatment plan when considering it as an adjunctive option.

Medical cannabis-related side effects

In the same way as many other forms of medicine, medical cannabis is associated with a variety of its own side effects. While it’s generally well tolerated, these side effects can include symptoms like dry mouth, dizziness and fatigue, so they may not be a suitable option for all patients. (17)

Unregulated vs. regulated medical cannabis products 

The ratio of CBD and THC contained in unregulated cannabis products, such as cannabis oils or CBD products, is often unknown in terms of both quality and quantity. (18)

These forms of treatment are not what this article has focused on - medical cannabis in cancer care is a regulated form of treatment, offering controlled dosages under clinically led guidance. 

How to guide UK-based cancer patients with confidence

When trying to find the best treatment plans for cancer patients, it’s important to prioritise two key elements: transparency and honesty. They are the ones looking to help manage their condition, after all, which is why it’s vital to understand the nuances involved in any potential treatment ideas they bring forward themselves, such as medical cannabis. 

The following is a recommended approach for oncologists to consider when managing their cancer patients:

1. Ask, don’t wait: Make medical cannabis a part of the conversation early on, and allow patients to do their own research.
2. Adapt your own treatment narrative: Treat medical cannabis the same as any other type of medication, outlining the associated benefits, risks and side effects as you would with other cancer-related treatments.
3. Don’t oversell its potential: Be honest about the current clinical evidence and the potential impact it could have on their overall quality of life or associated symptoms.
4. Check for interactions: Assess each patient’s individual medical history and any other treatments they’re currently taking before recommending it as a potential option.
5. Keep a track record: Only 20% of cancer patients tell their oncologist they’re taking medical cannabis. (1) So, if you know your patient is, keep a record and monitor how it’s being administered.

Delivering patient-centred cancer care with full transparency

Let’s be clear: medical cannabis isn’t a cancer treatment or cure of any kind. It simply offers a potential route for some patients to ease the burden of the side effects and secondary symptoms caused by cancer. But only when administered carefully and under the right kind of clinical supervision. 

The role of oncologists isn’t to have every answer. It’s to manage each patient individually, keeping on top of the latest related evidence and ensuring they are equipped with as much relevant information as possible to deliver effective treatment plans. Medical cannabis may form as part of that for some cancer patients. But it won’t be suitable for everyone.

We hope this article was helpful. For more information from Releaf, please visit their CPD Member Directory page. Alternatively, you can go to the CPD Industry Hubs for more articles, courses and events relevant to your Continuing Professional Development requirements.

References:

1. Phillips, C. (2024). As More People with Cancer Use Medical Cannabis, Oncologists Face Questions They Struggle to Answer. [Internet]. Available at: https://www.cancer.gov/news-events/cancer-currents-blog/2024/medical-cannabis-oncologists-patients-communication.  
2. Braun, I., Bohlke, K., Abrams, D., et al. (2024). Cannabis and Cannabinoids in Adults With Cancer: ASCO Guideline. J Clin Oncol. 42(3): 1575–1593. Available at: https://pmc.ncbi.nlm.nih.gov/articles/pmid/38478773/. 
3. Bar-Lev Schleider, L., Mechoulam, R., Lederman, V., et al. (2018). Prospective analysis of safety and efficacy of medical cannabis in large unselected population of patients with cancer. Eur J Intern Med. 49: 37–43. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0953-6205(18)30023-2.  
4. Cancer Research UK. (2024). Side effects of chemotherapy. [Internet]. Available at: https://www.cancerresearchuk.org/about-cancer/treatment/chemotherapy/side-effects.  
5. Cancer Research UK. (2022). Cannabis and CBD oil. [Internet]. Available at: https://www.cancerresearchuk.org/about-cancer/treatment/complementary-alternative-therapies/individual-therapies/cannabis. 
6. Grimison, P., Mersiades, A., Kirby, A., et al. (2024). Oral Cannabis Extract for Secondary Prevention of Chemotherapy-Induced Nausea and Vomiting: Final Results of a Randomized, Placebo-Controlled, Phase II/III Trial. 42(34): 4040–4050. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC11608591/. 
7. Blake, A., Wan, B., Malek, L., et al. A selective review of medical cannabis in cancer pain management. Ann Palliat Med. 6(Suppl 2): S215–S222. Available at: https://doi.org/10.21037/apm.2017.08.05.  
8. Zhou, E., Nayak, M., Chai, P., et al. (2021). Cancer patient’s attitudes of using medicinal cannabis for sleep. J Psychosoc Oncol. 40(3): 397–403. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC8511353/. 
9. Aggarwal, A., Erridge, S., Cowley, I., et al. (2025). UK Medical Cannabis Registry: A clinical outcomes analysis for insomnia. PLOS Ment Health. 2(8): e0000390. Available at: https://pmc.ncbi.nlm.nih.gov/articles/pmid/41662070/.
10. Cancer Research UK. (2023). Taste changes and loss of appetite. [Internet]. Available at: https://www.cancerresearchuk.org/about-cancer/coping/physically/diet-problems/types/taste-changes-and-loss-of-appetite.  
11. Razmovski-Naumovski, V., Luckett, T., Amgarth-Duff, I., et al. (2022). Efficacy of medicinal cannabis for appetite-related symptoms in people with cancer: A systematic review. Palliat Med. 36(6): 912–927. Available at: https://pubmed.ncbi.nlm.nih.gov/35360989/.
12. Rifkin-Zybutz, R., Erridge, S., Holvey, C., et al. (2023). Clinical outcome data of anxiety patients treated with cannabis-based medicinal products in the United Kingdom: a cohort study from the UK Medical Cannabis Registry. Psychopharmacology (Berl). 240(8): 1735–1745. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC10349732/.
13. Reddy, A., Hampton, J., Park, S., et al. (2025). Measuring the Effects of Cannabis on Anxiety and Depression Among Cancer Patients. 14(21): e71342. Available at:  https://onlinelibrary.wiley.com/doi/10.1002/cam4.71342. 
14. Salz, T., Meza, A., Chino, F., et al. (2023). Cannabis use among recently treated cancer patients: perceptions and experiences. Support Care Cancer. 31(9): 545. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC10585595/. 
15. Amin, S., Woo Chae, S., Kawamoto, C., et al. (2024). Cannabis use among cancer patients and survivors in the United States: a systematic review. JNCI Cancer Spectr. 8(1): pkae004. Available at: https://academic.oup.com/jncics/article-lookup/doi/10.1093/jncics/pkae004.  
16. Nayak, M., Revette, A., Chai, P., et al. (2022). Medical cannabis-related stigma: cancer survivors’ perspectives. J Cancer Surviv. 17(4): 951–956. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC10285009/. 
17. NHS. (2022). Medical cannabis (and cannabis oils). [Internet]. Available at: https://www.nhs.uk/medicines/medical-cannabis/.  
18. Bonn-Miller, M., Loflin, M., Thomas, B., et al. Labeling Accuracy of Cannabidiol Extracts Sold Online. JAMA. 318(17): 1708–1709. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC5818782/.