In 2013, Professor Wayne Hall presented a paper at an International Cannabis Policy Symposium hosted by the New Zealand Drug Foundation in Auckland. It was a review into 20 years of existing research into cannabis titled "What has research over the past two decades revealed about the adverse health effects of recreational cannabis use?".
So far, so uncontroversial.
But then the paper was published online in late 2014, and all of a sudden newspapers ran with alarmist headlines saying that cannabis "makes you stupid" and is "as addictive as heroin." These headlines, though, are simply not supported by the scientific evidence.
So what did the paper actually say? Among other things, it found that cannabis use may be harmful to health, and that the risk of developing dependence among those who have used cannabis across their lifetimes was slightly less than 10 per cent. The risk is lower among people who had used it for only one year and those who had used cannabis for ten years, with a two per cent and six per cent chance of developing dependence respectively.
But without context, these statistics mean little to most people. More problematically, only citing the addiction rate of cannabis without presenting the rates for other drugs is arguably a case of "cherry-picking the statistics for a purpose."
The evidence is clear. People who try cannabis are significantly less likely to become dependent than users of just about any other drug: the risk of dependence after a lifetime of use is 67.5 per cent for nicotine, 23.1 per cent for heroin, 20.9 per cent for cocaine, and 22.7 per cent for alcohol.
Instead of implying that cannabis and heroin dependence are equivalent, we should conceive of the use of drugs as being on a spectrum ranging from non-problematic to problematic use. The fact that the majority of cannabis use isn't harmful has significant implications for our cannabis policies.
But realizing that a majority of people do not come to harm by their own non-problematic cannabis use does not downplay the seriousness of problematic cannabis use.
This is particularly true for young people -- one in six adolescent users risk developing a dependence to cannabis. The New Zealand Drug Foundation has seen these problems first-hand and in response set up an innovative online self-help website, PotHelp. It acts as a tool for users who have had enough with their use and want to cut down or quit.
Based on a foundation of video testimony from everyday New Zealanders, a key aim of PotHelp is to assist visitors to acknowledge that change is possible. Providing online support for people with a drug dependency issue is showing early signs of being a valuable addition to treatment provision in New Zealand.
However, for all the harm that can come from cannabis use, even more can come from its criminalization. Many of the stories featured on PotHelp identify the criminal nature of people's addiction and the associated stigma as a reason that they failed to seek help sooner.
Under the current strict prohibition framework, the 90 per cent of people who don't develop cannabis dependency are unnecessarily harmed and the remaining 10 per cent are treated as criminals when in fact they should be treated by health professionals. Our approach needs to shift from being predominantly criminal justice based towards a health and social focus.
International Centre for Science in Drug Policy
We Need to Get the Facts Right on Cannabis Addiction