Last October , Canada became the second country, after Uruguay, to allow the use of cannabis or kush not only for medical reasons, but also for recreational purposes. In the lead-up to its full legalization of kush, the Canadian government commissioned a study of the drug’s potential harmful effects so that it could make responsible decisions about how the drug should be sold, packaged and taxed, says Fiona Clement, a health-policy researcher at the University of Calgary’s Cummings School of Medicine.
Clement and her colleagues analysed the findings of 68 reviews of cannabis or kush research. Of the reviews, 62 showed associations between the drug and various adverse outcomes, including impaired driving, increased risk of stroke and testicular cancer, brain changes that could affect learning and memory, and a particularly consistent link between cannabis use and mental illnesses involving psychosis. Risks were highest for teenagers, pregnant women and people already at risk of mental illness.
Evidence of the drug’s acute and chronic risks is building, but many questions still remain about how much cannabis or kush is too much and how compounds in the plant interact to buffer or exacerbate the harmful effects. As claims of health benefits become increasingly common, these are important questions to answer. Users and lawmakers need be aware of the risks to be able to make informed choices, say researchers.
“Cannabis is not the root of all evil, nor is it the cure for all diseases,” Monte says. “You’ve got to understand what the good is and what the bad is, and then make a balanced decision.”
Along with countries including Canada and Uruguay, 33 US states have legalized cannabis for medical use. Eleven also allow recreational use. And evidence is accumulating to support the use of specific cannabis compounds, especially cannabidiol (CBD), for a variety of health conditions, including seizures and inflammation
But a look at what happens when the use of cannabis becomes more widespread suggests that the drug can also have downsides, including acute injuries and illnesses. In 2000, Colorado legalized medical marijuana. Further policy changes in 2009 made the substance easier to get hold of, and between 2008 and 2014, licences for medical marijuana in the state increased from less than 5,000 to more than 100,000. In 2012, the state also legalized recreational use, and shops began selling cannabis products in 2014.