This paper accompanies the report Medical use of cannabis and cannabinoids — questions and answers for policymaking and summarises the findings of major systematic reviews of the evidence on the effectiveness and safety of cannabis and cannabinoids when used to treat symptoms of various medical conditions. It provides more detail on topics summarised in the main report, in particular on the sections on the available evidence on the effectiveness of medical use of cannabis and cannabinoids and those on the health risks and potential unintended consequences associated with the medical use of cannabis and cannabinoids.
The first section of this paper summarises in detail the conclusions of three influential peer-reviewed publications (Koppel et al., 2014; NASEM, 2017; Whiting et al., 2015). These reviews evaluated all the published evidence on the efficacy and safety of cannabis for multiple medical uses. They used a clearly specified search strategy to identify studies, clear rules for deciding which studies to include and exclude, standardised criteria for evaluating the degree of bias in the studies and explicit criteria for synthesising the overall evidence.
The paper then summarises the findings of systematic reviews and meta-analyses of the evidence on the effectiveness of cannabinoids in treating chronic pain; chemotherapy induced nausea and vomiting in cancer patients; appetite stimulation in HIV/AIDS; intractable epilepsy; and palliative care for cancer. All these reviews used explicit search criteria, standardised tools for assessing study bias and explicit methods of synthesising the overall findings. Their degree of agreement is also summarised in a table.
A third section summarises reviews of the adverse effects of medical use of cannabis as indicated in randomised controlled clinical trials. The section includes the results of a meta-analysis of adverse effects reported in clinical trials conducted by Whiting et al. (2015). The section also considers long-term harms reported among recreational cannabis users that may be potential adverse effects of long-term medical use of cannabis and cannabinoids.
Finally, the paper includes an overview of studies, primarily conducted in the US, that explore the potential unintended consequences of the medical use of cannabis and cannabinoids.
Cannabis and cannabinoids have been made available in a wide range of forms, and the various products and preparations tended to be described in different ways in different publications. While the main report uses a new typology in describing the different forms in which cannabis and cannabinoids are made available, we have chosen in the background paper to use the original terminology from the studies under consideration.