Science still unsettled on cannabis health effects

The general election aside, the referendum over the legalisation of recreational cannabis is also exciting some debate as parties and individuals take positions for or against the proposition.

One thing that strikes me immediately is that the cannabis referendum is quite different from the euthanasia referendum. Amajority vote for the End of Life Choice Act will bring it into effect. Voters know what they are getting. The legislation has already passed through Parliament.

Not so with the cannabis referendum. There is a draft bill which voters can study, but none of the proponents of legalisation are saying that this is the bill Parliament will pass if there is amajority vote in the referendum. They can’t say that because no-one can guarantee what the new Parliament will do. There may be significant amendments, so voters are less sure of the outcome and rightly more wary.

The third aspect of the referendum that interests me is the science underlying the proposition that cannabis is a ‘‘good’’ drug to have in the community.

Like most people I had assumed that the science on the matter was largely settled. When I delved into it, I found that this was very far from the case.

In fact, an extensive review of the scientific literature undertaken in the United States found that the medicinal value of cannabis is still subject to significant and unresolved question marks.

Equally, the recreational merits, while widely endorsed bymany users, are also open, particularly regarding the long-term effects on brain development in younger people.

The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research is amulti-disciplinary study by the US National Academies of Science, Engineering and Medicine, a premier research body. All its reports are an evidence-based consensus of expert opinion and are peer reviewed.

Its panel of 16 experts from science and medicine looked at over 10,700 studies published in English from 1999 to 2016. It provides a comprehensive consolidation of knowledge about the effects of cannabis across 11 separate health endpoints.

Its finding are instructive. In essence it says that we cannot conclusively statewhether cannabis works medically or recreationally; there is evidence both for and against. The report states: ‘‘Despite the extensive changes in policy at the state level and the rapid rise in the use of cannabis both for medical purposes and for recreational use, conclusive evidence regarding the short- and longterm health effects (harms and benefits) of cannabis use remains elusive.

‘‘A lack of scientific research has resulted in a lack of information on the health implications of cannabis use, which is a significant public health concern for vulnerable populations such as pregnant women and adolescents.

‘‘Unlike other substanceswhose use may confer risk, such as alcohol or tobacco, no accepted standards exist to help guide individuals as they make choices regarding the issues of if, when, where, and how to use cannabis safely and, in regard to therapeutic uses, effectively. ‘‘

In short, we don’t know enough to statewhether cannabis is safe or not; whether it works as claimed by users, or whether its merits outweigh its risks.

The National Academies study used a rating system of the evidence rating it from ‘‘conclusive’’ to ‘‘substantial’’ to ‘‘moderate’’, ‘‘limited’’ to ‘‘little or no evidence’’. It examined 16 medical conditions. Only for treating chronic pain in adults was there ‘‘substantial evidence’’ cannabis worked. To treat cancers, including glioma, the evidence was ‘‘insufficient’’ either way. Evidence that cannabis worked in chemotherapy and HIV/ AIDS was also ‘‘limited’’.

For the treatment of epilepsy, irritable bowel syndrome, Huntington’s disease, Parkinson’s and schizophrenia or schizophreniform psychosis the evidence of cannabis’ value was ‘‘insufficient’’. For Tourette’s, dementia and clinician-measured spasticity the evidence was ‘‘limited’’.

On whether cannabis use is associatedwith heart attack, stroke, diabetes, asthma and lung diseases the study says the evidence is ‘‘unclear’’ and ‘‘insufficient’’.

Cannabis impairs cognition and memory and ‘‘during adolescence is related to impairments in subsequent academic achievement and education, employment and income, and social relationships and social roles’’. There is ‘‘no evidence’’ that cannabis works to treat drug addiction.

The report went on to identify awide range of areas where further research was needed to form better conclusions. The lack of comprehensive field trials has long been noted in scientific literature, along with the difficulty of doing properly controlled studies of the use of an illegal substance.

These findings give me little confidence that we know enough about what this drug does to our health. Perhaps the health outcomes are just one factor to be considered – pro-legalisation groups certainly think so. But I’d argue that health outcomesmust surely be front and centre in any conclusions we reach about this drug.

The lack of comprehensive field trials has long been noted in scientific literature.