Professor David Finn:

May I have two minutes to respond to an important point by Deputy Durkan on the root causes of pain? Of course, for many chronic pain patients, the root cause may be known. It may be rheumatoid arthritis, osteoarthritis, an accident or post-operative pain. Where possible, the best approach is to try to address the root cause, modify the underlying disease and have a disease-modifying approach to the treatment of the pain. However, for a great many chronic pain patients the root cause is not known, particularly for neuropathic pain patients, for example, where there is no underlying disease, incident or accident to which that pain can be traced back. That type of pain, particularly neuropathic pain, is really difficult to treat and it is refractory to many of our current medications. There is some evidence that cannabinoids may be helpful to a subset of those patients.

Is it disease-modifying? That is debatable. We know that the root cause of that type of pain is peripheral and central sensitisation, the increase in synaptic plasticity in the pain pathway, the strengthening of synaptic connectivity in the spinal cord and the brain. There is good evidence that cannabinoids can reduce those things - they can reduce peripheral and central sensitisation. Are cannabinoids and cannabis a panacea, a cure-all for everything? Absolutely not. It will not be suitable for every patient or even every chronic pain patient.

It could be an option for those patients who are refractory to current treatments, who do not do well on current treatments or who are experiencing unacceptably high numbers of side effects, perhaps from current treatments. I would not recommend that anyone ignore the advice of his or her consultant. I attach great importance to and emphasise the consultant's expertise. I certainly recommend that all patients heed the advice of their consultant in this or any other arena.

Reference was made to one patient who did not respond well. That does not surprise me. I do not know anything about the patient in question or the type of cannabinoid product that was taken. Whether someone will respond or not depends on many factors. It depends on the type of patient, his or her medical history, the exact type of pain and the length of time for which it has been experienced, whether there are other comorbidities, and the type and exact composition of the cannabinoid being taken. One must determine whether it is THC, cannabidiol or other constituents. These factors need to be taken into account and known. Of course, as scientists we cannot come to any conclusion based on low-end numbers and individual patients. We must examine objectively the evidence in larger patient groups and studies.

Whether THC and cannabidiol themselves are enough or medical cannabis and the plant extract are needed is a big question. There is some belief that there is an entourage effect with the plant. What I mean by that is that the cannabinoids and constituents in the complex plant material may combine in some way that we do not yet fully understand to have a greater therapeutic benefit in certain indications - greater than just THC or cannabidiol on its own. That is a subject for research. More research is needed on that, for sure. There is some evidence, however, that in some cases there can be a greater therapeutic benefit by virtue of having the complexity of the plant and the entourage effect versus just one or two of the molecules on their own. I refer to the possibility that the molecules can interact so cannabidiol, which does not induce euphoria or the same types of psychoactive effects that THC induces, can attenuate and dial down some of the psychoactivity of THC. That ratio is really important.

Regulation is key. This is not for me and my expertise is not in legalities or how the Houses or Government would go about regulation, but I do believe regulation is very important. It is a question of the extent. Does one opt for continual monitoring to be able to know with certainty what patients are taking what products and what doctors are prescribing so they may be regulated tightly?