Professor David Finn:

In response to Senator Swanick's question about the exacerbation of paranoia and the presence of cannabinoid receptors in the amygdala in the brain, that is an area we have done a lot of research on in Galway. The literature on cannabinoids, anxiety, paranoia and psychosis is somewhat complex. It depends exactly which cannabinoid, which constituent of the plant we are talking about. There is some evidence that high THC containing cannabis may exacerbate paranoia and, of course, any doctor who would consider prescribing medical cannabis or cannabinoids to a patient would want to take into consideration the psychiatric history of the patient, particularly any history of psychosis or paranoia. It is likely that if such a history were present cannabis would not be the most appropriate course of action for that patient. There is evidence that some of the high THC containing products, cannabidiol does not act at CB1 or CB2 receptors but is still present in significant quantities in cannabis may reduce anxiety, paranoia and psychosis.

The balance of THC to cannabidiol, the ratio of the two, will be really critical. I would concur with Dr. O'Grady's comments on the essential need to label the products correctly and in detail so that the patient and the doctor know exactly what they are prescribing or taking in terms of THC content, cannabidiol content, but also some of the other cannabinoids that are present in significant quantities too. Many of the 700, or 114, if one likes, cannabinoids are present in very low or trace concentrations and there is a question mark over precisely what sort of effect they may be having on the body and their efficacy. The mechanisms of action for each and every one of those hundreds of compounds has not been elucidated but we do have a significant body of knowledge around the use of cannabis going back over hundreds if not thousands of years and understand quite a lot about its effects on the body, in the context of misuse, recreational use and more recently in that of medical use. The possibility of exacerbating paranoia could be dealt with by taking into account the history of the patient. If there is a history of paranoia or psychosis, it is possibly contraindicated.

As to whether it might precipitate paranoia or psychosis - although the question was not asked, we should maybe talk about this - the evidence is mixed. There is evidence to suggest there may be a moderate effect of cannabis inducing or precipitating psychosis in those at risk.

If one starts using it early in life, during adolescence or as a teenager, and perhaps if there is a genetic background or predisposition to psychosis, cannabis likely precipitates psychosis and, potentially, schizophrenia. However, and Dr. Barnes has written on this and will probably speak on it, with the majority of users of cannabis, either in the recreational or medical setting, schizophrenia and psychosis are not major concerns if the use is monitored carefully and if there is no prior history or genetic predisposition.

Deputy Kelleher asked about co-morbidities and adjunctive treatment. Many of the studies on cannabis and cannabinoids have been in the adjunctive treatment setting, where medical cannabis or cannabinoids have been studied alongside the patient taking additional medicine, for example, opioids for chronic pain or anti-spasticity drugs for multiple sclerosis, MS. There is good evidence from the scientific literature and basic science studies to suggest that there might be some synergistic interactions between cannabinoids and some of the other medicines, particularly the opioids, where the two drugs working together might produce a synergistic beneficial therapeutic effect more so than either drug alone. By giving lower doses of each drug, cannabinoids and opioids, one might get a greater and additive therapeutic effect which allows one to reduce some of the side effects of both classes of drugs. That is interesting in terms of drug interactions, which is probably the origin of the question.

With regard to co-morbidities, the MS patient group has been well studied. There are multiple symptoms there ranging from spasticity to neuropathic pain and other symptoms. There is good evidence that cannabinoids and medical cannabis can reduce the spasticity and the neuropathic pain that was experienced by many multiple sclerosis patients.

I agree with what Dr. O'Grady said about the risks of diversion. We should continue to monitor studies coming from the US and other countries that have made the move towards legalising medical cannabis, but so far the studies suggest that the diversion issue is not a major concern.

I hope that is helpful.