Scores of drugs with unknown risk profiles have slipped through

you say that these chemicals are structurally similar, you’re also saying that others aren’t – and pointing the way for future drugs.” Prohibition was hard enough in a world where governments knew what drugs to ban. Now, in a world where new drugs appear every week, it seems altogether impossible. While the rest of the world is cranking up the treadmill, New Zealand has decided to get off. Last year, The Psychoactive Substances Bill passed both houses of parliament with only a single dissenting voice. Reading the bill to parliament, associate health minister Peter Dunne explained that prohibition simply couldn’t keep up with the turnover of new drugs. “Scores of products with unknown effects and unknown risk profiles – indeed, some barely known to science at all – have slipped through this regulatory void,” he said. “This proliferation of poorly understood chemicals and their widespread use should concern us all. So we need an enduring solution.” The details of his proposed solution are still a little hazy, though some basic rules have been set out. The most important is that drugs won’t be allowed on the market unless they have a proven “low risk of harm” – though exactly what that means and how it will be decided are still a work in progress. Drugs also won’t be sold to under-18s, at convenience stores, or anywhere alcohol  is also on sale. Labels with ingredients  and health warnings will be mandatory. Existing illegal drugs won’t be legalised, but Peter Dunne says this could be done later. A new authority charged with implementing the regime is still working out the other details. The law is expected to come into full effect very soon. In the meantime, New Zealand is in a halfway house. When the law was enacted in July, legal highs that had been on sale for at least three months could apply for temporary licences; 46 were approved and six refused, based on an assessment of risk. Retailers also had to apply for licences to continue selling those drugs. From an estimated 3000 outlets, the authority granted 110 licences. Until the new regime goes live, there are many unanswered questions about how it will operate. The biggest is how to decide which drugs are suitable for sale. Exactly what constitutes “low risk”? For the past 15 years, David Nutt, a neuropsychopharmacologist at Imperial College London, has been trying to answer that question. His approach takes into account harm to individuals, the risk of addiction and harms to society. “You come to a sensible balance,” says Nutt. “You look at the bigger picture.” By this reckoning, the most harmful drug is alcohol, followed by heroin and crack cocaine (The Lancet, vol 376, p 1558). But finding a way to assess and compare drug harms is only half the problem. The  next step is deciding where to draw the line. Nutt liaised with the New Zealand regulators on this question. “I told them they should set the threshold as ‘less harmful than alcohol’ but they laughed and said that’s too harmful,” Nutt says. He now suggests “half  as harmful as alcohol” would make sense. Wherever the line is set, the next challenge is how to prove a drug is on the right side of it. Stewart Jessamine, head of Medsafe, New Zealand’s version of the US Food and Drug Administration, says the initial requirement will be similar to the “phase 1” safety data pharmaceutical companies must provide before they can do large-scale clinical trials.