Cannabinoids, the main chemicals found within the cannabis plant, have been shown to affect pain transmission signals from the site of pain, up the spinal cord and to the brain. In addition to this they have also been demonstrated to affect the emotional processing of pain itself.
However, there is a lack of high-quality evidence on the effects of pharmaceutical grade cannabis on chronic pain in humans. As such, there are no licensed medical cannabis preparations for chronic pain. Therefore, whilst chronic pain is the most common reason why medical cannabis is prescribed in the UK, it is only available privately.
Estimates suggest that 1.4 million people in the UK purchase illicit cannabis for health reasons, with chronic pain and arthritis being the third and fourth most common reasons why.
Studies from North America suggest that in some jurisdictions where cannabis has become available, this has been associated with a reduction in prescriptions of opioids.
No studies have sought to examine if there is any relationship between cannabis use and healthcare utilisation in UK patients with chronic pain secondary to osteoarthritis.
This study will use GP data from individuals with osteoarthritis who are known cannabis consumers and compare their outcomes to patients who do not have any recorded cannabis use. The main aims are to compare the quantity of opioid pain medications and other pain medications between each group. This will help inform our knowledge of the impact of cannabis consumption on managing the pain associated with osteoarthritis.
In pre-clinical studies, cannabinoids derived from cannabis have been shown to reduce the transmission of nociceptive signals, whilst also impacting central sensitisation, increasing inhibition of ascending signals and modifying the emotional and cognitive manifestations of pain in the brain. They have also demonstrated anti-inflammatory effects.
The current clinical evidence on the effects of cannabis on chronic pain, however, is typically of low-quality and is highly heterogenous. There has only been one Phase 2A randomised controlled trial on a medical cannabis preparation for osteoarthritis to date, specifically. Consequently, there are no licensed preparations of medical cannabis for osteoarthritis-associated chronic pain, meaning people who want to use cannabis for this reason must access unlicensed medical cannabis preparations, or rely upon self-medicating via illicit channels.
The aim of this study is to compare differences in outcomes between individuals with osteoarthritis with a known exposure to cannabis, with those with no recorded exposure to cannabis using primary care data. Exposed patients will be identified by pre-defined clinical codes, and subsequently matched with unexposed control patients.
The outcomes of interest will include a comparison of the incidence of opioid prescribing, incidence of strong opioid prescribing, annual oral morphine equivalent dose per day of supply, incidence of other prescription medications for pain, and primary care healthcare utilisation. Comparisons between each group will be conducted utilising an independent t-test or Mann-Whitney U test as appropriate.
The outcomes of this study will for the first time provide information on the pain-specific impact of exposure to cannabis on individuals with osteoarthritis in the UK. This will help inform future research to address the unmet need of limited available treatments for osteoarthritis-associated chronic pain. It can also be utilised to inform harm reduction strategies for people consuming cannabis illicitly for health reasons.
The primary outcomes of interest are:
- Prevalence of opioid prescribing;
- Incidence of opioid prescribing;
- Annual oral morphine equivalent dose per day of supply;
- Incidence of high and very high opioid dose prescribing
Key secondary outcomes include:
- Prevalence of other prescription medications for pain;
- Incidence of other prescription medications for pain;
- Average number of primary care consultations per year;
- Average number of primary care consultations related to osteoarthritis per year
Mikael Sodergren - Chief Investigator - Imperial College London
Simon Erridge - Corresponding Applicant - Imperial College London
Joht Singh Chandan - Collaborator - University of Birmingham
Krishna Gokhale - Collaborator - University of Birmingham
Mikael Sodergren - Collaborator - Imperial College London