Professor David Finn:

The omission of pain as one of the indications in the HPRA report is controversial. I was surprised. Given the meta-analysis and systematic reviews that have been published, including the Barnes report, which we have discussed, but also papers from Whiting et al., Hill et al. and the National Academies of Sciences, Engineering and Medicine, pain is the condition that has been most studied in terms of cannabinoids. A substantial body of evidence suggests moderate efficacy or, depending on the study and the condition, better-than-moderate efficacy in some cases. It is a pity that chronic pain was omitted. The HPRA gave four reasons for doing that and the Irish Pain Society's statement examined and commented on them. I will run through the commentary quickly.

The first reason was that the causes of chronic pain are diverse and that a suitable patient population or clinical indication for treatment with cannabis cannot be defined due to the complexity and variety of chronic pain syndromes. We have learned quite a lot in the past 15 or 20 years about the mechanisms and causes of chronic pain. Central sensitisation and peripheral sensitisation are well recognised as the neurobiological bases for chronic pain. As has been shown in many studies, cannabinoids work to reduce these two mechanisms. The clinical research to which I alluded have shown that cannabinoids have moderate-to-significant efficacy in terms of chronic pain, including neuropathic and cancer pain. Sativex has been licensed in Canada for neuropathic pain in MS and for cancer pain, so there is a precedent for that type of drug, namely, a cannabinoid medicine that has passed the usual hurdles that a medicine must jump over in order to be authorised for chronic pain. In other jurisdictions that have authorised medical cannabis, its primary use is for chronic pain. In Colorado, 84% or 90% of patients reported their main reason for using medical cannabis as being chronic pain.

The second reason in the HPRA's report was "physical, emotional, social, spiritual and other subjective factors inform the individual pain experience, making it difficult for a doctor to objectively assess the effectiveness of treatment". The complexity of a disease is not a reason to avoid treatment. A pain consultant would be able to assess the effectiveness of a treatment. Otherwise, how could we justify prescribing any drug for chronic pain if doctors were not able to assess their efficacy? The efficacy of cannabis and cannabinoids could be assessed.

The third reason was that there was "a large number of authorised medicines that are of proven effectiveness, and other non-pharmacological treatments available to treat the many factors involved in chronic pain". This is true. There are many other analgesic drugs for and non-pharmacological approaches to the treatment of pain, but we cannot ignore the fact that one in five people in Europe suffer from chronic pain. In Ireland, the figure is approximately the same. Depending on the study, it is between 13% and 35% of patients. This is the case despite the availability of other treatments. The largest study ever carried out on this matter in Europe involved 46,000 patients.

The study, Survey of chronic pain in Europe: Prevalence, impact on daily life, and treatment, by H. Breivik et al, showed that 40% of chronic pain patients said that their pain was inadequately managed by current treatments. This illustrates that there is a massive unmet clinical need here. Existing drugs are working well for some patients but they are not working well for all. That may be because of lack of efficacy or unacceptably high levels of side effects.

The fourth reason the HPRA gave was that chronic pain is common and the potential use of cannabis-based medicines by a large number of patients raises concerns about misuse and diversion into the wider community. I understand those concerns but when we look at countries that have introduced medical cannabis, we can see that there is no significant evidence that this has led to diversion and misuse or to an increase in the overall recreational use of cannabis. The other point is that those concerns about diversion and misuse are not unique to cannabis and cannabinoids. They certainly apply to opoids and benzodiazepines. Opoids involve a greater dependence liability and probably present a greater harm to the individual and society overall than cannabis and cannabinoids. This addresses Deputy Boyd Barrett's question. It is very difficult to objectively compare side effects of one class of drugs with those of another. It is hard for me or anyone else to say whether one is worse than the other. Certainly, the risk of overdose with opoids and benzodiazepines is significantly higher than for cannabis. There are very few, if any, documented cases of fatality due to cannabis overdose. The dependence liability relating to cannabis is generally thought to be less than that of opoids. Depending on the study, the percentage of people who use opoids for chronic pain and who become dependent on them is around 3% but it could be as high as 10%. The risk of overdose also exists. Does that answer the questions?