NRT: What are the headline findings from the report for people working with brain and spinal injury clients?
MB: There is now good evidence to show that cannabis, including the non-psychoactive component CBD, can help to treat chronic pain – such as that experienced post spinal or brain injury – spasticity, nausea and vomiting and anxiety. We also found moderate evidence that it helps to stimulate appetite, which may also be relevant to neuro-rehab units. There was limited evidence to support cannabis’s role in alleviating depression and in brain protection in the context of traumatic brain injury.
What about the risk of schizophrenia associated with cannabis use?
Most literature supports a causal hypothesis between cannabis use and psychosis, particularly if usage starts at an early age and if the individual has a genetic predisposition to psychosis. It is unlikely that any one environmental factor (such as cannabis use) or any one gene can cause schizophrenia on its own. It appears that cannabis is a component cause in the development of symptoms of schizophrenia and the onset of this mental illness depends upon many interacting factors. However, it is also important to remember that most people who use cannabis do not develop schizophrenia, and most people with schizophrenia have never used cannabis.
It is likely that THC is the main cannabinoid which triggers schizophrenia and psychosis. CBD on the other hand is known to be anti-psychotic and may have a therapeutic role as an anti-psychotic agent although further studies are required.
What impact does cannabis have on chronic pain?
Current treatment for severe chronic pain is often effective but can be associated with serious side effects. Opioids, for example, carry very serious risks, including mortality. Chronic pain is one of the leading reasons for medical use of cannabis in the UK. It is known that the endocannabinoid system is one of the key bodily systems that regulate pain sensation with actions at all stages of the pain processing pathway. Neural signalling through both CB1 and CB2 receptors has a key role in normal pain processing and considerable animal model and pre-clinical data on both patients and healthy volunteers confirm that modulation of the endocannabinoid system can reduce pain. Cannabis products nabilone, dronabinol, nabiximols and smoked marijuana have all been shown to be efficacious to varying extents in a variety of pain settings in good quality studies. We concluded that there is good evidence for efficacy of cannabis for pain relief in various formulations and in a number of settings.
Could cannabis play a greater role in the management of spasticity after spinal and brain injuries?
There is good evidence for the efficacy of the cannabis extract nabiximols for reducing patient-reported spasticity symptoms, although there is not firm evidence for improvement in objective measures. We consider there is good evidence of safety in the long-term and for continued efficacy. We also consider there is moderate evidence for the efficacy of oral cannabis extract for reducing patient-reported spasticity scores. There is insufficient evidence to make any recommendations with regard to other forms of cannabis. One study we considered assessed the effect of nabilone on spasticity after spinal cord injury (Pooyania et al 2010). The research involved 11 subjects who either received nabilone or a placebo during a four-week period and after a two-week washout, subjects were crossed to the opposite arm of the study. There was a significant decrease on active treatment for the Ashworth score in the most involved muscle as well as the total Ashworth score. There were no significant differences in secondary measures which included the spasm frequency scale and the clinician’s and subject’s global impression of change. Side effects were mild and tolerable.
Anxiety is particularly prevalent with people coming to terms with severe injuries. Could they benefit from cannabis?
Cannabis can both increase and decrease anxiety in humans. CBD has been shown to reduce anxiety whereas THC, the psychoactive part of the drug, usually has the converse effect. Overall, we consider there is good evidence for CBD use in anxiety. This evidence base includes a double-blind, randomised, placebo-controlled clinical study led by Bergamaschi in 2011. It showed that orally-administered CBD was associated with a significant can’t reduction in anxiety, cognitive impairment, and discomfort in patients suffering from generalised social anxiety disorder subjected to a simulated public-speaking test. A further study carried out by Crippa and colleagues (2011) looked at the effect of CBD on anxiety and the brain mechanisms involved. This double-blind, randomised, placebo-controlled study found that CBD significantly decreased anxiety and that this was related to its effects on the limbic and paralimbic brain areas. Improved anxiety levels have also been reported in patients suffering from chronic neuropathic pain (Ware et al 2010b).
What conclusions did you draw about cannabis and epilepsy?
There is certainly a theoretical basis to suggest that cannabis could have implications for epilepsy. While animal model and early human studies are promising, however, at the moment robust trials are lacking but further results are awaited. So there is only limited evidence currently.
In which other areas related to neuro-rehab would you like to see more studies carried out in future?
There is a theoretical basis to suggest cannabinoids could provide neuroprotection in the context of traumatic brain injury, but as yet, evidence is limited and unconvincing. There is no evidence to support neuroprotection in stroke and, in fact, limited evidence shows that heavy recreational users have a slightly increased risk of stroke. So further clarity in these two areas could be hugely beneficial to neuro-rehab professionals. It was also surprising to discover that, despite a long history of cannabis use in headache and migraine, there are no good quality randomised clinical trials. I would like to see more studies into neuropathic headaches in particular.
What regulatory hurdles are stopping people benefitting from the medicinal properties of cannabis?
We currently have a shambolic situation in which the very recognition of cannabis as a medicine has potentially delayed its obtainability by people who really need it by several years. Until October this year, CBD was legal to purchase in the UK. Then the MHRA [Medicines and Health Care Products Regulatory Agency], which is sponsored by the Department of Health, said it now recognises that CBD could potentially have medicinal value and should be considered a medicine. This is dependent, however, on manufacturers providing proof of its efficacy. Therefore, individuals, including young children with resistant epilepsy, may not be able to legally obtain CBD in the near future. They won’t be able to until the producers can satisfy the regulations for medicinal products, which will take some years.
Is this situation likely to be resolved anytime soon?
It’s only a matter of time before the UK government legalises cannabis for medical purposes as we are so far behind the rest of the world now. Several more American states have just voted to legalise it there, while it is also now legal in at least 10 European countries. We are way behind on this and conflicted because of this nonsense with the rescheduling of CBD.