Chronic pain is a condition that affects a significant proportion of the population, with estimates suggesting that somewhere between 1 in 10 and 1 in 15 people are affected globally. In the UK, however, it is estimated that between 35.0-51.3% of the population may experience chronic pain at some time in their lives. Chronic pain patients often experience a range of additional symptoms, as well as poor quality of life, sleep, and mobility.
Despite this high prevalence, the current medications are largely considered ineffective at managing the condition in the long term and often carry a significant risk of misuse, addiction, and overdose in addition to undesirable side effects. Therefore, there is a serious need for alternative therapies and treatment options to manage the condition.
Increasingly, patients and clinicians alike are showing their interest in utilising the potential pain-relieving properties of the cannabis plants and its derivatives. Data collected through the UK Medical Cannabis Registry was recently assessed to determine how cannabis-based medical products (CBMPs) may be useful in the treatment of chronic pain and associated symptoms.
Current Treatment Options for Chronic Pain
There are currently a limited number of pharmacological options for the treatment of chronic pain. For example, the National Institute for Health and Care Excellence (NICE) exclusively recommends the use of antidepressant medications for the management of chronic primary pain.
However, the pharmacological management of chronic pain in a clinical setting often involves the use of medications that NICE describes as having “insufficient or poor-quality evidence to support their use”, including opioid analgesics. Opioid-based medications are widely used for many aetiologies of chronic pain, yet, randomised controlled trials (RCTs) involving opioids have largely been performed in acute settings, with limited evidence supporting their use for chronic pain management.
Medical Cannabis and Chronic Pain
Cannabis is an ancient crop that has been used medicinally – including for the treatment of pain conditions and as an anaesthetic – for thousands of years. However, the prohibition of cannabis led to a significant gap in our clinical knowledge of the plant. Nonetheless, a growing number of observational studies and randomised controlled trials are beginning to, once again, explore the potential of the cannabis plant and its derivatives in the treatment of chronic pain and other pain-related conditions.
Observational studies have identified associations between medical cannabis treatment and significant reductions in pain severity and interference and improvements in overall health-related quality of life measures. However, RCTs have largely been of indifferent quality, leading to conflicting conclusions. A growing number of patient registries have been set up to address the current gap in research.
Patient registries offer an increasingly important source of observational data, providing evidence in a resource-efficient manner within a real-world setting. The UK Medical Cannabis Registry (UKMCR) was established in December 2019 to prospectively collect data of patient outcomes, allowing assessment of the benefit-risk profile of CBMPs for the treatment of a variety of medical conditions, including chronic pain.
The Current Data from the UK Medical Cannabis Registry
Baseline questionnaires captured demographic data as well as details of patients’ medical history, including primary, secondary, and tertiary conditions for which they had received a prescription for CBMPs. The incidence of comorbidities included hypertension, depression and/or anxiety, arthritis, epilepsy, and endocrine dysfunction. Parameters including drug and alcohol data, smoking status, and past cannabis use were also recorded.
Data regarding CBMP prescriptions – including manufacturer, formulation, route of administration, and CBD/THC concentrations – were recorded. Adverse events were either self-reported by each patient at each follow-up or were recorded following disclosure to their clinician during a routine visit.
Outcome Measures and Results
A number of outcome measures were used, including the Brief Pain Inventory short form (to measure pain severity and interference), the Short-form McGill Pain Questionnaire-2, Generalised Anxiety Disorder-7 (used to generate a score for severity of anxiety), EQ-5D-5L tool (used to determine the overall health-related quality of life (HRQoL)), the Sleep Quality Scale (SQS), and finally, the VAS pain scale (to capture how severely patients are experiencing their pain).
Of the total of 289 patients who had completed at least some quantity of the registry process, 190 were eligible for inclusion in the final analysis. Of these, 135 patients had recorded patient-reported outcome measures (PROMs) at 1 month, 68 had recorded PROMs at 3 months, and 44 had recorded PROMs at six months.
Pain & Quality of Life Measures
Overall, patients exhibited statistically significant improvements at one, three, and six months in anxiety (GAD-7), sleep (SQS), the EQ-5D-5L pain and discomfort subscore and EQ-5D-5L Index Value. Furthermore, improvements were observed at months 1 and 3 for EQ-5D-5L mobility, and EQ-VAS subscores, while a significant improvement was observed at 1 month follow-up for EQ-5D-5L anxiety and depression subscore.
Statistically significant improvements were also observed in Brief Pain Inventory (BPI), SF-MPQ-2, and VAS scores across all time points. These results suggest there was a reduction in pain severity, interference in day to day activities, and neuropathic pain.
These data from UKMCR demonstrate a potential association between initiation of medical cannabis treatment and improved outcomes in pain-specific and general health-related quality of life measures, over a short to medium term. Statistically significant improvements were observed in multiple domains, including pain and discomfort, anxiety and depression, and sleep quality scales.
Adverse Events & Opioid Administration
Of the patient sample, 43 (18.7%) patients reported at least one adverse event, with 20 (8.7%) patients reporting two or more adverse events. The most commonly reported adverse events were nausea (n=11; 5.8%) and fatigue (n=6; 3.2%). A significant proportion (49.3%) were considered mild, while 30.7% were moderate and 18.7% were severe.
The UKMCR also recorded the median oral morphine equivalent doses of patients prescribed opioid medications. At baseline, this median oral morphine equivalent was 24.0mg in this group. No significant differences were observed in oral morphine equivalent doses after one month; however, a significant reduction in median oral morphine equivalent was observed at three months (n=15; median of differences = -15.00mg), and six months (n=10; median of differences = -10.50mg).
The authors of this assessment conclude that initiation of treatment of chronic pain with CBMPs is associated with significant improvements in self-reported pain-specific and general HRQoL outcomes in the short to medium term in this patient cohort. However, they note that numerous limitations with the study design restrict the “capacity to draw definite conclusions regarding causality and the efficacy of treatment.”
Nonetheless, significant improvements were observed in relation to health-related quality of life, alongside an acceptable adverse event profile in comparison to other widely used treatment options for chronic pain. Furthermore, the apparent reduction in opioid doses also demonstrates promise, though further analysis in this area is required in the future.