Cannabis has been an important part of ancient medicinal traditions for thousands of years. This impressive crop has been utilised for the treatment of countless ailments, from pain to glaucoma. Since ancient times cannabis has continued to be used in an increasingly varied way. There are now countless anecdotal reports that cannabis is beneficial for the treatment of a huge number of illnesses and conditions, with one of the most controversial claims being that medical cannabis can be used to treat cancer.
Given the sheer length of our relationship with cannabis, you would think that we would now know everything there is to know about this divisive plant. But the fact is, we don’t – far from it in fact. An inconveniently timed global prohibition of cannabis in the 20th century meant that scientific research into the potential benefits and harms of cannabis was severely stunted. The resulting lack of high-quality evidence has created the perfect conditions for individuals and organisations on both sides of the cannabis argument to make bold and, as yet unproven, claims about cannabis.
The question is: what evidence does exist? Is the idea that cannabis can be used to treat cancer just another baseless claim or is there evidence to support it?
Cannabis as a treatment for cancer
Historically, the rate of cannabis use among cancer patients is significantly higher than that of the general population. One survey, conducted by a US-based online support group, Breastcancer.org, found that 42% of respondents (women with breast cancer) reported using cannabis products; however, only 23% stated that this was specifically for medicinal purposes with the remaining respondents using cannabis both medicinally and recreationally. Nonetheless, patient interest in medicinal cannabis remains high. For example, in the same study, 64% of 612 respondents expressed extreme interest in the medicinal use of cannabis.
While it is difficult to know exactly how long cannabis products have been utilised for cancer-related symptom relief, legal access to medicinal cannabis for this purpose dates back only a few decades. In 1996, California became the first US state to legalise medical cannabis. This law change enabled various patients – including those with cancer – to use cannabis without fear of prosecution for the first time since the pre-prohibition era.
Since 1996, the legalisation of medical cannabis has spread throughout the US and many other parts of the world. However, in many jurisdictions, medical cannabis is currently only recommended for a small number of applications. For instance, in the UK, the National Institute of Health and Care Excellence (NICE) only recommends the prescription of medical cannabis products for a handful of conditions: treatment-resistant epilepsy, spasticity related to Multiple Sclerosis, and chemotherapy-induced vomiting and nausea.
How could cannabis be useful for cancer treatment?
While NICE recommendations may currently only recommend medical cannabis for nausea and vomiting associated with cancer treatment, it may also be useful for other cancer-related symptoms. Due to the high number of cancer types, symptom profiles can vary significantly; however, some of the most common symptoms of cancer and related treatment include pain, nausea and vomiting, and loss of appetite. Furthermore, a number of studies have aimed to assess the potential of cannabis and its derivatives in treating cancer itself and improving patient quality of life.
Chemotherapy-induced vomiting and nausea
A number of studies have assessed the anti-emetic potential of cannabis – many of which have placed a specific focus on chemotherapy-induced nausea and vomiting. One study, published in Annals of Oncology in 2020, observed a significant improvement in the occurrence of nausea and vomiting with the addition of a THC:CBD medical cannabis preparation. Moreover, 83% of participants preferred the medical cannabis preparation to placebo. Finally, no serious adverse events were attributed to the administration of THC:CBD. Such findings have contributed to improved access to medical cannabis for this specific cancer-related effect.
In some countries, medical cannabis preparations may be considered for the management of cancer-related pain when other first-line therapies have failed to yield satisfactory relief. While anecdotal reports suggest that cannabis could be useful in this application, current clinical evidence does not entirely reflect this. For example, a large clinical study conducted between 2010 and 2013 concluded that, while Sativex (THC:CBD) was more effective than placebo at controlling cancer-related pain, this wasn’t clinically significant.
However, another study, published in 2022 found that patients who initiated medical cannabis use earlier achieved a reduction in opioid use and improved pain control when compared with patients with delayed start cannabis use. Further investigation is required to fully understand the potential of medical cannabis in the management of cancer-related pain.
Loss of appetite and wasting
Cancer patients often experience a loss of appetite and muscular wasting (cachexia), which may be associated with disease progression or cancer treatment. The perception that cannabis use enhances appetite is well reported; however, there is still a lack of high-quality clinical evidence to support this. Nonetheless, in some jurisdictions, including the US, medical cannabis may be considered to stimulate appetite in patients with HIV. It is therefore theorised that medical cannabis preparations could also be useful for stimulating appetite and managing cachexia in some cancer patients.
Quality of life
Medical cannabis is increasingly being considered as a resource for improving quality of life – particularly in palliative care. As is often the case with medical cannabis, clinical evidence remains limited, with existing studies yielding varying results. However, there is some evidence to suggest the potential of cannabis-based products for improving quality of life.
For example, the results of one study concluded that regular cannabis use was associated with improvements in quality of life in cancer patients. Various other studies assessing quality of life in patients with other conditions have also identified some benefits of medical cannabis use.
The anti-cancer potential of cannabis and cannabinoids
Aside from being used for symptom management, there is a growing interest in the potential of medical cannabis for the prevention and treatment of cancer itself. A number of studies have aimed to assess this potential in a clinical setting.
In one study, researchers assessed the effects of Sativex in combination with the chemotherapy drug, temozolomide in patients with recurrent glioblastoma (an aggressive type of cancer that affects the brain and spinal cord). They found that a higher proportion of patients were alive after one year of using Sativex (83%) compared with those taking placebo (44%).
However, the vast majority of research into the anti-cancer potential of cannabis has been laboratory-based, with few assessing cannabis preparations in-vivo. Nonetheless, a number of these studies have yielded promising results. For example, in 2019, researchers at Harvard University reported that a flavonoid found in cannabis, known as FBL-03G was seen to kill cancer cells in the pancreas and other areas of the body. Another study found that “CBD can induce cell death and enhance radio-sensitisation of glioblastoma.”
Medical cannabis treatment for cancer in the UK
Since the rescheduling of cannabis in the UK in 2018, medical cannabis products have been available for the treatment of several conditions. However, current guidelines significantly restrict the prescription of medical cannabis through the NHS. Moreover, current NICE guidelines only recommend the use of cannabis-based medicines in relation to cancer for chemotherapy-induced nausea and vomiting.
Nonetheless, the growing presence of private medical cannabis clinics across the UK has significantly improved patient access to medical cannabis products for the treatment of cancer-related symptoms and for palliative care.
Potential risks and side effects of medical cannabis
While current studies – including those mentioned in this article – have yielded some impressive results regarding the potential of medical cannabis, it is important to also be aware of the potential side effects associated with medical cannabis treatment. In many cases, side effects are deemed to be mild or moderate and cannabis is often concluded to be well tolerated in patient samples. Common adverse events associated with cannabis treatment include dizziness, dry mouth, nausea, behavioural and mood changes, and feeling tired.
When initiating medical cannabis treatment, your clinician should also be aware of any possible drug-drug interactions that may increase the risk of any complications. For example, additive effects can occur when medical cannabis is taken in combination with sympathomimetics, central nervous system depressants such as alcohol and opioids, and anticholinergics.
The key take-aways
In recent years, a number of studies and trials have uncovered various mechanisms through which cannabis-based medicines may be useful in the treatment of cancer. From symptom management to potential cancer-killing abilities, our understanding of this potential is slowly improving. However, current high-quality evidence remains limited and there is a clear need for more clinical studies in this area.
Nonetheless, medical cannabis treatment is available in the UK and a number of other countries around the world for the management of cancer-related symptoms. Specialist clinicians may be able to advise on the potential benefits and risks of medical cannabis treatment for cancer patients, including potential drug-drug interactions. For more information regarding access to medical cannabis, check out our guide to medical cannabis prescriptions in the UK.