Introduction

Cancer pain occurs in 20% to 50% of all cancer patients, and up to 80% of those with advanced disease experience moderate to severe pain. Most often, the pain is a direct result of the cancer or the cancer treatment, and severely reduces quality of life through physical and emotional suffering, impairment in functioning, and can cause depression or requests for assisted suicide in some cases. Effective management of cancer pain would avert all unnecessary hospital admissions and improve patient outcomes, however, the challenges in assessment and the risk for opioid misuse complicate the treatment.¹

Medical cannabis, particularly Cannabis sativa, has been studied in oncology as part of treatment for symptoms of cancer, including pain. Tetrahydrocannabinol (THC) and cannabidiol (CBD) are two cannabinoids that engage the endocannabinoid system (ECS), leading to potential analgesic (pain relief) effects; this emerging treatment option is being embraced by a growing number of patients and clinicians as an alternative, or adjunct, to conventional approaches to pain management. Clinicians are encouraged to be aware of the therapeutic benefits and of the possible risks of cannabis to adequately guide patient care.²

Understanding cancer-related pain

Cancer pain management is essential to the improvement in the quality of life of patients who feel discomfort for many different reasons, such as the cancer itself and the treatments, including chemotherapy, surgery, and radiotherapy. Pain can be caused by damage to nerves, inflammation, or side effects of drugs used in the treatment of cancer. These patients often develop peculiar kinds of pain, depending on the treatments involved, such as bone ache from certain drugs or peripheral neuropathy because of chemotherapy. The effective management thereby helps in the understanding of the nature, severity, and precipitating factors of pain, with individualised treatment approaches usually involving medications like NSAIDs, opioids, among other analgesics. Acupuncture, physical therapy, and the teaching of relaxation skills are non-pharmacological interventions that could provide symptom relief and a sense of control during therapy.¹

Management of cancer pain becomes more complicated in older adults. Comorbid conditions, drug sensitivities, and impaired communication may increase the risk of undertreatment or the development of adverse effects. Healthcare providers generally initiate pain medications at a lower dose in these patients to prevent complications and monitor them carefully for side effects related to their central nervous system, such as drowsiness, constipation, or changes in cognition. These resources are further augmented by complementary therapies, palliative care, and integrative approaches, such as acupuncture and hypnosis. In all, a holistic approach to cancer pain control- one that balances medical, psychological, and lifestyle interventions- can significantly enhance comfort and overall well-being in cancer patients, especially those with advanced disease.¹

What is medical cannabis?

Medical cannabis refers to the products prepared from the Cannabis sativa plant and are used to address various health issues. Over 540 chemical compounds have been isolated from Cannabis sativa, the chief active components being cannabinoids, mainly THC and CBD. The chemical compound THC is psychoactive and responsible for the "high" produced in marijuana. CBD does not produce psychoactive results. Plants that contain less than a certain level of THC are considered industrial hemp rather than marijuana.

While the Food and Drug Administration (FDA) has not approved the cannabis plant as medicine, the agency has approved some cannabinoid-based drugs. Examples include Epidiolex, a purified form of CBD approved for treating some forms of rare epilepsy, and synthetic THC medications Dronabinol and Cesamet are approved to treat nausea and vomiting accompanying chemotherapy and for appetite loss in HIV/AIDS patients, respectively. Others have reported that cannabis is helpful for chronic pain and symptoms of multiple sclerosis, although findings have been inconsistent, and some reports note only modest benefits.

Mechanism: how medical cannabis alleviates pain

Cannabis relieves pain in cancer through many different mechanisms. Cannabinoids, such as THC and CBD, act upon the ECS through cannabinoid receptors (CB) 1 and 2 located throughout the brain, nerves, and the immune system. The activation of CB1 receptors in the central nervous system decreases pain perception through the modulation of pain signals, while CB2 receptors located on immune cells have a function in reducing inflammation, which is often at the root of the pain in cancer patients.³

Besides analgesic effects, cannabis acts upon the emotional and cognitive components of pain processing. Various studies suggest psychoactive effects produced by THC allow patients to detach themselves from pain and experience less interference in their daily life. Additionally, cannabis use is associated with improved sleep and mood, both of which impact pain tolerance and overall quality of life. Therefore, cannabis addresses pain from a holistic approach; cannabis addresses physical pain and, importantly, much of the psychological and emotional stress associated with chronic pain in cancer.³

What the research says about medical cannabis for cancer pain

Recent clinical studies have demonstrated that medical cannabis could be a useful complementary therapy for the alleviation of cancer-related pain. In a cross-sectional study among 252 patients with refractory cancer pain, about 70% reported subjective improvement with medical cannabis, and almost 40% noted significant improvement in coping with their illness. In general, side effects were mild, with the most common being fatigue and dizziness.⁴

An observational study was made to evaluate the effectiveness of medical cannabis in cancer-related pain.  The reductions in pain scores were at 3, 6, and 9 months from the start of medical cannabis treatment. Patients with chronic pain could reduce the level of pain medication consumed over time. Products with a balanced content of THC and CBD were more effective than products dominated by either one of the cannabinoids.⁵

While results appear promising, several shortcomings were noted regarding existing research. One study described the existence of very few high-quality randomised controlled trials (RCTs) and greater availability of studies of an observational nature. Product variability derived from cannabis complicates the process of standardisation and comparison across studies.⁶

Despite these limitations, the available evidence suggests cannabis might be a useful option in cancer pain relief, especially for patients refractory to conventional treatments. More robust clinical evidence from large-scale RCTs is needed if the full efficacy, safety, and optimal use of cannabis for cancer pain management are to be determined.

Medical cannabis in the UK

Medical cannabis was legalised in the UK in November 2018, largely because of public demand, especially high-profile cases where children with severe epilepsy were concerned. Currently, NICE allows limited prescription for conditions like multiple sclerosis spasticity, chemotherapy-induced nausea, and severe epilepsy through some cannabis-based products for medical use (CBMPs), such as Sativex and Epidiolex. Nevertheless, access remains highly restricted, with a small number of prescriptions issued by the NHS so far.⁷

Despite the processes of legalisation, obstacles still involve limited medical training in cannabis prescription, often very restrictive guidelines, and physician concerns regarding efficacy and possible side effects. The majority of patients in search of CBMPs are being referred to private prescriptions, usually with hefty costs. To further advance access, healthcare experts call for more clinical research, better-balanced prescribing guidelines, and physician education so that patients who could benefit from medical cannabis have access to it within safe and regulated environments.⁷

Summary

Medical cannabis appears to be a safe and effective treatment for pain in cancer patients who are resistant to classical analgesic treatment. Activating the endocannabinoid system with cannabinoids, such as THC and CBD, could reduce physical pain, decrease inflammation, and ameliorate mood and sleep factors considered critical in improving quality of life in cancer patients. However, due to the complexity of cannabis-based therapies and possible variable individual responses, patients must consider such benefits against potential risks, including major side effects of fatigue and dizziness, in consultation with healthcare providers. Although various access and regulatory constraints persist, a greater evidence base and increased support for medical cannabis continue to fuel its complete integration into the management of cancer pain, an element of fresh hope in dire patients needing alternative treatments.