Despite the fact that herbal cannabis is being used by many patients for arthritis symptom relief, and although the medical use of cannabis has been legalised in certain countries, most doctors (including me) know very little about the subject.
This years American College of Rheumatology meeting included an excellent and timely update which could be summarised as follows;
Lab based research
There is some evidence to suggest that cannabis derived substances (cannabinoids) may alter certain types of pain response, and reduce some of the immune response, in animal models of arthritis. Altering the processing of ‘endocannabinoids’ (substances which are made naturally in response to pain) may also alter the response to pain in this setting.
Despite this promising evidence from the laboratory, no good quality research (a randomised controlled trial) has yet been performed using herbal cannabis in humans. There have been a couple of small, uncontrolled studies which have suggested possible improvements in certain arthritis symptoms (pain and sleep for example) but with significant side effects (see below).
Part of the problem is that herbal cannabis contains over 60 cannabinoids (and hundreds of other compounds) and it is not yet certain which of these might be effective. Also, the strength of these components varies widely between products and their absorption varies considerably from person to person. Thus far, it hasn’t been possible to separate the analgesic properties from the psycho-active ones.
A more targeted approach has involved the use of certain subtypes of synthetic cannabinoids.
Rheumatoid arthritis and Fibromyalgia
Studies performed using these compounds in rheumatoid arthritis (an oral spray called Nabiximols – containing the cannabinoids, THC and cannabidiol) and in fibromyalgia (an oral preparation known as Nabilone) resulted in some improvement in pain and sleep but were still associated with significant side effects – especially drowsiness. These formulations are not licensed for the treatment of arthritis pain but are available in certain countries for the treatment of other conditions (such as MS and neuropathic pain).
Whereas there is a common perception that smoking or ingesting cannabis is relatively safe, information presented at the meeting suggests that regular use can result in significant side effects which are listed below.
Cannabis results drowsiness, reduced short term memory, selective attention and reduced reaction times for up to 5 hours after using. Whereas this may not be perceived as a problem for recreational users, it may pose significant problems for those using cannabis regularly for pain relief who want to drive. Use of cannabis doubles the risk of dying in a road traffic accident, and is the most commonly used drug in up to 7.6% of people seriously injured in motor accidents.
Smoked or ingested cannabis can cause hypotension (low blood pressure) and increases the risk of having a myocardial infarction by a factor of five. For those who already have angina, it reduces exercise capacity by 50%. There is evidence suggest that regular cannabis smoking doubles the risk of lung cancer and may damage the lungs over time (especially regular use begins earlier in life).
Whereas cannabis can reduce the symptoms of anxiety in some, it can cause anxiety or depression in others. This is particularly true in those with either a personal history or family history of mental illness.
The Bottom line
Evidence suggests that manipulating the cannabinoid system may be a useful approach for the relief of certain symptoms in rheumatic disease but the session concluded that more research should be done to clarify the mechanisms of these effects.
This risk benefit profile of inhaled herbal cannabis indicates that it should not be recommended for the treatment of pain arising from arthritis.
Where used, cannabinoids should be reserved for patients with pain refractory to standard medical treatment.
Pharmacologic preparations are more desirable than largely uncontrolled herbal use.
Who should avoid cannabinoids?
Because of these risks (and others) the presenters suggested that these compounds should be especially avoided in the following;
Young people, especially those under the age of 25 (who are particularly at risk of dependance)
Anyone with a history of psychiatric illness or substance abuse (or those taking another psycho-active drug)
Those with history of cardiac disease or liver disease