Politicians and police agree that drug-checking at music festivals is probably a good idea. So why is it still illegal?

Episode six looks at why it's so hard to do the right thing, when the right thing is keeping young people alive.

"You're seeing the praying mantis that rules the world, but you have the strength of ten men."

It seems likely that at this summer's music festivals, on both sides of the Tasman, there will be drug-checking to let people know what they're taking and whether it's dangerous. Senior politicians, doctors and police officers have told us it's a good idea.

It's also illegal.

People have taken drugs at music festivals for as long as there have been music festivals. But in the last 15 years, things have changed. As policing has made the principal recreational drugs more difficult to manufacture, hundreds of new drugs have emerged. All of them are less well understood than the old drugs - some of them are markedly more dangerous.

Wellingtonian Wendy Allison has been quietly carrying out drug-checking for the past eight years, initially for friends. A night in 2014 when people around her lapsed into "eight to 10 hour psychotic breaks" after taking what they believed to be MDMA (Ecstasy) was a turning point.

She began offering the service in a more organised way and recording her results - and they were alarming. Fewer than 20 per cent of the pills or powders tested were what the owner believed they'd bought. But half of the people who were told they didn't have what they thought chose not to take the drugs at all.

"I don't know of any other intervention that actually does that."

"In terms of reducing potential harm, that's immediately half of the people taken out of harm's way."

David Caldicott, Emergency Consultant at the Calvary Hospital in Canberra, has seen similar results in the years he has been coordinating drug-checking at events and nightclubs in Australia. But he faces a challenge this summer, as the New South Wales government threatens to prosecute doctors who take part in a trial of drug-checking at larger festivals.

Emergency medicine specialists are on the frontline of the problem. Dr Paul Quigley of the Wellington Hospital emergency department explains to us the chaos he's seeing with drugs like 25i-NBOMe, which has largely supplanted the safer-but-harder-to-manufacture LSD in New Zealand…

Go to this episode on rnz.co.nz for more details