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