Do cannabinoids have a role in cancer pain?
Much of the content of this article is taken from a talk given by Dr Paul Farquhar-Smith (Consultant in Pain Management and Anaesthetics, The Royal Marsden NHS Foundation Trust) at the ASPCP annual conference in November 2018.
Cannabis has been used as pain relief in many ancient cultures including China and India. Nicholas Culpeper, a 17th-century herbalist, described it as ‘easing the pain of the gout, the hard humours of knots in the joints, the pains and shrinking of the sinews, and the pains of the hips’. It is often said, although probably not substantiated, that Queen Victoria used cannabis for relieving the pain of menstruation and childbirth.
Cannabis plants contain over 400 cannabinoids. Of most interest to researchers are the non-psychoactive CBD and the psychoactive THC. CBD can be bought in high street shops such as Holland and Barrett. It comes as oil in a dropper bottle or capsules. THC-containing products are not legal in the UK.
Cannabinoid receptors are found in the brain and spinal cord. Cannabis is known to be stored in the fatty tissue of the brain and this would explain the many affects felt by users of cannabis, including euphoria (high), heightened sensory perception, impaired cognition and memory, distortion of time sense and fragmentation of thoughts, to name a few.
There have been animal studies looking at cannabis binding in various kinds of pain; these indicated that in animals, the cannabinoid does bind to receptors. In terms of research on humans, there isn’t a huge amount of published research. There are a number of meta-analysis reports referenced in the link.
The trials were conducted in all kinds of pain, but the trials for cancer pain are, understandably, even fewer. The conclusion seems to be that there is variable benefit. The main issue, which in turn led to poor compliance, was the side effects of cannabis, especially nausea and drowsiness. In many cases, this outweighed any benefit.
The UK government has decided that medicinal cannabis will become a legal drug, and can be prescribed by specialist doctors from 1st November 2018 to patients who have been appropriately medically assessed. This new legislation will not limit the types of conditions that can be considered for treatment with cannabis-based medicines, but there is anecdotal evidence to support its use for patients, including children, with treatment-resistant seizures and other conditions.
The decision to prescribe cannabis-based medicines must be made by a specialist doctor – a consultant, not a GP. Consultants focus on one field of medicine such as neurology or paediatrics and are listed on the General Medical Council’s specialist register. They must make decisions on prescribing cannabis-based products for medicinal use on a case-by-case basis.
Cannabis-based medicines are currently unlicensed and so they should only be used when the patient has a special clinical need that cannot be met by licensed products. The clinician would be expected to take full responsibility of risks and liability for treatment.
The only licensed medicine in the UK currently is Sativex, which contains THC and CBD. There undoubtedly will be many more products coming to market now that cannabis has been put into the ‘medicinal use’ category – in fact there is news of a couple of products already. Two products available in other countries could potentially become available in the UK in time but there is still negotiation going on at Department of Health and Home Office level before this happens. At present, a patient with a personal import licence issued by the Home Office may be able to obtain one of these but would have to collect it personally from its country of origin.
With the psychoactive effects of THC not always being well tolerated, CBD could provide a viable alternative. The potential uses of CBD have also been studied and there are many claims for analgesic activity without the psychoactive component. This too requires more research.
Ashtons offers a half-hour presentation which would suit any staff who are interested, as well as doctors and nurses. For more information please speak to your visiting pharmacist.