Ireland: HRB publishes findings on safety and efficacy of medical cannabis

Ireland’s Health Research Board (HRB) has published the findings from its review of evidence for the safety and efficacy of prescribed medicinal cannabis.

The report, which was published on Tuesday 23 January, found evidence to support the use of prescribed medicinal cannabis for certain conditions for which it is currently approved in Ireland, including nausea and vomiting in cancer and spasticity in multiple sclerosis. 

There was also ‘promising’ evidence of a significant benefit for neuropathic or nerve pain, which can occur with conditions such as multiple sclerosis, diabetes or spinal cord injury.

For most other conditions, including anxiety and pain in conditions such as cancer, rheumatic diseases and fibromyalgia, there is ‘no conclusive evidence’ to confirm the efficacy of prescribed medicinal cannabis, according to the report. 

Regarding the safety of prescribed cannabis, the review found that although serious adverse events do not appear to be common, there is some evidence that some side effects such as dizziness, dry mouth, sedation, and headache can occur. 

Mixed evidence was found on the likelihood of other adverse events such as drowsiness, nausea, and any psychiatric disorder adverse events.  

The study was carried out as part of a Department of health review of the current Medical Cannabis Access Programme (MCAP).  Currently only patients living with one of the three qualifying conditions, chemotherapy-induced nausea and vomiting, treatment-resistant epilepsy, and spasticity associated with MS, are able to access cannabis-based medicines through the scheme, which was launched in 2019.

Dr Kathryn Lambe, Research Officer at the HRB and lead author of the report, says: “Our review indicates there is some evidence to support the use of prescribed medicinal cannabis in conditions such as nausea and vomiting due to chemotherapy, spasticity in multiple sclerosis, and managing neuropathic pain. 

“However, for most other outcomes, the findings were inconsistent at best. This review will help inform decision making in relation to future policy on the use of prescribed medicinal cannabis along with input from patient groups, clinicians, and service planners.”

Recommendations for future research 

Covering research conducted over the last 30 years on the use of prescribed medicinal cannabis by adult patients only, the study evaluated evidence from 47 reviews, across a number of medical conditions ranging from cancer, multiple sclerosis and rheumatic diseases, to pain, mental health and neuropsychological conditions.

It focused on evidence related to prescribed medicinal cannabis containing natural or synthetic CBD or tetrahydrocannabinol THC or their derivatives.

The authors concluded that the body of research they examined was ‘fragmented’ with a ‘low degree of certainty in the evidence for most outcomes’. 

They made a number of recommendations for future research in order to improve the quality of clinical data on medicinal cannabis. This includes subgroup analysis for different types of pain, the use of modern treatments as active comparators rather than placebo, and studies with different treatment arms to define the optimal ratio of THC and CBD for the indication of interest.

Informing future policy 

According to the report, the findings will inform the Department of Health’s position on the suitability of cannabis-based products for various clinical indications, as well as future responses to communications concerning the prescribing of cannabis based products.

Chief executive of the HRB, Dr Mairead O’Driscoll, said: “It is essential that healthcare policy is informed by the latest evidence, including in areas where existing research is not sufficiently developed to draw robust conclusions. By conducting this kind of review over time, the HRB can continue to provide policy makers with evidence to inform their decisions as research evolves.”

A ‘missed opportunity’

The MCAP has previously received criticism from patients for its ‘restrictive’ nature, with fewer than 100 people thought to be enrolled on the scheme so far. The outcome of the HRB review has cast doubt over whether the programme will be expanded any further.

Patient advocates have expressed disappointment that it did not include real-world evidence or engage with Irish patients who are reporting benefit from medical cannabis—many of whom have travelled abroad to access it. 

“The HRB report highlights the need for more detailed analysis of medical cannabis,” says legal researcher and drug policy advocate, Natalie O’Regan.

“In 2024 we are still hearing ‘the need for more research’ as a reason to not expand access. The report failed to engage with any current MCAP patients, and missed the opportunity to gather real-world data that is available on their doorstep. At the end of the day, it is patients who will suffer the consequences of limited access to a medicine that they may find invaluable.”

She added: “One good point was the report found evidence that supports medical cannabis in neuropathic pain, which I hope it will extend to in the near future.”