Those alarmed by next year's referendum on whether recreational cannabis use should be legalised often assume it will lead to increased use. This would be troubling indeed, given our already high intake.
A 2015 Global Drug Study found that, in the previous 12 months, more Kiwi respondents had smoked pot (32.5 per cent) than tobacco (30.1 per cent). But the fact is, legislation has failed to persuade potheads to turn over a new leaf, it's here and it's here to stay.
What has sparked more use has been popular culture - cue, almost certainly, Bob Marley's visit in 1979 and, perhaps, cult movie Goodbye Pork Pie two years later.
Marijuana rolled up on New Zealand's shores via merchant ships from the early 1950s, but some was probably already in suburban backyards – among jazz and literary coteries in Auckland and Wellington.
One likely impact on New Zealand use is the availability of other drugs. The much more alarming rise in methamphetamine appears to have, anecdotally at least, resulted in a decline in marijuana in some communities.
Massey University Illicit Drug Monitoring System (IDMS) showed the change occurred between 2015 and 2016 as meth became cheaper and easier to access. The report found a sharp decline in the availability of cannabis during the same period.
To be blunt, what hasn't traditionally impacted rates of use is law and enforcement. One WHO study in 2008 included data from New Zealand as representing Oceania and found: "Globally, drug use is not distributed evenly and is not simply related to drug policy, since countries with stringent user-level illegal drug policies did not have lower levels of use than countries with liberal ones."
Legalisation or decriminalisation in countries such as the US, Canada and Portugal has apparently led to some small increases, although it is hard to tell whether these rises may have occurred anyway. In Colorado, youth use has been stable since legalisation in 2015, interrupting a rising trend.
Justice Minister Andrew Little recently commented a referendum "informed by a thorough factual public debate will lead to a result likely to be more credible and accepted".
Could it be that the spectre of increased use is one of the first fallacies to be weeded out?