This evidence review, examining the efficacy and safety of medicinal cannabis for a range of conditions, aims to support the 2022 review of the Medical Cannabis Access Programme in Ireland. The synthesis will also inform Department of Health responses to communications concerning the prescribing of cannabis-based products, and inform the Department’s position on the suitability of cannabis-based products for various clinical indications.

Review questions
• Question 1: What is the evidence for the clinical efficacy of medicinal cannabis in the treatment of the conditions/clinical indications of interest among adults?
• Question 2: What is the evidence for the safety of medicinal cannabis in the treatment of the conditions/clinical indications of interest among adults?

Methods
This evidence review comprises an overview of reviews (umbrella review). The methods used in this review are divided into five stages: identifying research evidence; screening of search results; data extraction; quality assessment; and synthesis. From a terminology viewpoint, we use the term ‘medicinal cannabis’ rather than ‘medical cannabis’ in this evidence review for consistency, as an umbrella term to include both pharmaceutical cannabis-based medicines and cannabis plant and its preparations used for medical purposes. We acknowledge the varied understandings of these and other terms used to describe cannabis-based products for medical use, as well as the diversity of opinions as to which terms are most appropriate.

Release
The study was conducted to inform a Department of Health review of the current Medicinal Cannabis Access Programme (MCAP). It found evidence to support the use of prescribed medicinal cannabis for certain conditions for which it is currently approved in Ireland, such as nausea and vomiting in cancer and spasticity in multiple sclerosis. There was also 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. Regarding the safety of prescribed medicinal 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, however, on the likelihood of other adverse events such as drowsiness, nausea, and any psychiatric disorder adverse events.

Commenting on the findings, HRB Chief Executive 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.”

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.”

Covering research conducted over the last 30 years on the use of prescribed medicinal cannabis by adult patients only, the study evaluated evidence 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 cannabidiol (CBD) or tetrahydrocannabinol (THC) or their derivatives.

About the Medicinal Cannabis Access Programme
The Medical Cannabis Access Programme (MCAP) enables a consultant to prescribe a cannabis-based treatment for a patient under their care for a small number of conditions, where the patient has not responded to standard treatments. The conditions included in the MCAP are spasticity associated with multiple sclerosis, intractable nausea and vomiting associated with chemotherapy, or severe, refractory (treatment-resistant) epilepsy.
The cannabis-based products included under the MCAP are produced in line with good manufacturing practice and have been assessed by the Health Product Regulatory Authority as being suitable for medical use. These products include CBD oil drops, oral solutions, and cannabis flower.