Banning drugs is a failure, and governments should instead be helping users learn their limits, an expert says.
Global Drug Survey founder Dr Adam Winstock believes people who use drugs can do so safely, if they are taught how.
"The problem is there aren't really any sensible guidelines on how many drugs you can do in any space of time without running a high risk of ruining your life."
The British psychiatrist, addiction medicine specialist and researcher says the evidence base for a zero-tolerance to drugs is "probably just about zero".
The annual Global Drug Survey is again being supported in New Zealand by Stuff.co.nz.
From Monday, Kiwis can join more than 100,000 people around the world expected to take part in the online survey.
TAKE THE SURVEY: Global Drug Survey 2016
Winstock's got the support of the New Zealand Drug Foundation, which agrees prohibition is outdated - and it's only a matter of time before decriminalisation begins here.
From last year's survey, Winstock created the world's first "safer use limits" for cannabis, an online tool for users to identify how at-risk they are, based on their consumption level and frequency of use. More than 15,000 people have already taken the test.
He's planning similar tools for alcohol, cocaine, ketamine and MDMA.
While the only way to avoid all harm was to avoid drugs, the risk could be "massively reduced for most people" if they followed the right health advice, Winstock said.
Thanks to long-time government support for needle-exchange programmes, New Zealand now has among the world's lowest rates of HIV transmission through needle use, with just two people diagnosed last year.
Drug Foundation executive director Ross Bell said politicians could go a lot further, by supporting "drug-checking services" at festivals and nightclubs, "where users can scrape off a bit of their pill, or a drop of the liquid they've got, and have that tested, and verified 'this is ecstasy, or this is something else, or this is quite dangerous and we recommend you don't take it'."
However, Bell believed a slow shift in drug policy was coming, with cannabis decriminalisation likely to be the first cab off the rank. Police were already issuing pre-charge warnings, instead of convicting those in possession of the drug, while the government was slowly warming to the idea of medicinal cannabis use.
"We're going to look back on the zero-tolerance approach, and laugh at it, in the same way [we banned] same-sex marriage, or giving women the vote. We're going to look at prohibition and say 'were we serious about that? Did we really think that was the way to go?'," Bell said.
"I think the right system would be removing the criminal penalties and replacing them with health interventions, so that if you were a dependent drug user, instead of getting a conviction, you'd get referred to treatment."
Down the track, he says, cannabis could be regulated under the Psychoactive Substances Act, which covers synthetic cannabis and party pills.
"I don't know how fast it might happen here. I think if you look at some of the signals in the National Drug Policy, the government is very clear: they're not going to decriminalise drugs anytime soon, but they're beginning to signal about getting the legal balance right ... are there other ways of dealing with possession offences? So it could happen sooner than you think, and I think this is inevitable around the world."