November 2017

Health impacts of cannabis – benefits, harms and many unknowns

A new report by Royal Society Te Apārangi summarises what is known about the potential risks and benefits to health from the use of recreational and medicinal cannabis.

It finds evidence that cannabis-based medicines have some therapeutic effect in specific clinical situations and that recreational cannabis use can have some negative health outcomes. The report finds large knowledge gaps in understanding the health effects of both recreational cannabis and cannabis-based medicines, particularly in specific groups of the population, and this lack of knowledge poses a public health risk.



Royal Society Te Apārangi President Professor Wendy Larner says the report draws heavily on the 2017 publication by the US National Academies of Sciences, Engineering and Medicine: The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations as well as additional literature of relevance to Aotearoa.

“With changes to New Zealand’s legislation on prescribing cannabis and the upcoming referendum on whether New Zealand should legalise recreational cannabis, Royal Society Te Apārangi has prepared this report to assist people considering the opportunities and risks to health associated with cannabis use.” These are the best pipes for smoking.

Associate Professor Joe Boden, Department of Psychological Medicine, University of Otago, who was one of the report’s reviewers, says that for medicinal cannabis, there is evidence of effectiveness to treat a small number of specific conditions but the evidence is not well established as it hasn’t been widely tested in clinical trials.  “Cannabis-based medicines have been shown to have some therapeutic effects in treating chronic pain, nausea from chemotherapy, muscle spasms due to multiple sclerosis and in rare forms of epilepsy, but we don’t have good evidence that they work better than the existing medicines available to treat these conditions.”

Dr Irene Braithwaite, Medical Research Institute of New Zealand, who also was a reviewer of the report, says that cannabis-based medicines, many of which are derived from plant material, have not been through the same vigorous efficacy or safety testing as existing medicines. “The levels and types of cannabinoids in these plant-based preparations can vary greatly due to different growing, harvest and storage conditions. This makes it difficult to draw conclusions by comparing or pooling the results from the limited number of studies that do exist,” says Dr Braithwaite.

For recreational use, some harms are also seen. “Recreational cannabis is associated with negative outcomes including mental illness, particularly in youth, drug use disorders, respiratory illness, impaired cognition, increased road accidents and lower birthweight in babies born to women exposed to cannabis,” says Professor Michelle Glass, Head of the Department of Pharmacology and Toxicology at University of Otago. “People may assume cannabis is largely safe as it has been used by people for so long, but this is not necessarily the case.”

The report finds many gaps in the research literature, particularly in population groups thought to be at most risk from cannabis use: those under 18 years, pregnant and breastfeeding women, people over 50 years and heavy cannabis users.

An area where the risks are clear is synthetic cannabis, says Professor Glass, who studies cannabinoids in her research.

“Calling it synthetic cannabis is misleading as it’s not cannabis. It’s non-cannabis plant material sprayed with lab-made chemicals that mimic the effect of cannabis in the body but tend to be much more powerful. In 2017 there were approximately 45 deaths linked to synthetic cannabinoids in New Zealand and every day, ambulance services in New Zealand report multiple life-threatening cases related to synthetic cannabinoid use.

“Being so different to cannabis, it can be difficult to identify with standard drug screening techniques.”

Professor Glass says it is worth noting that synthetic cannabis would remain illegal, regardless of the outcome of the public referendum, such is its great potential to cause harm.

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