Methamphetamine use is back on the rise as the price of the illegal substance comes down.
The results are part of a survey of police detainees which also found there is now a cannabis drought.
Last year Chris Wilkins and his team interviewed 800 people in police custody, asking them about their drug usage.
"What we found was an increase in methamphetamine use amongst the police arrestees that we interviewed," he told Newshub.
Around 38 percent of the 800 interviewed said they'd used meth in the last year, up from 26 percent in 2010.
Mr Wilkins says the availability of the drug is increasing while the price has fallen, dropping $168 a gram in just two years.
Earlier this month, the Chief Coroner revealed that 20 people have died from using synthetic drugs this year.
Mr Wilkins says there's evidence a black market has emerged from the 2014 legal high ban.
"One of the interesting things is we found increasing synthetic cannabis dependence, increasing strength of synthetic cannabis," he said.
"There seems to be the effects of the development of this black market."
The Drug Foundation's Ross Bell says the report makes for some tough reading.
"We've got a whole lot of problems around a whole lot of different drugs and our approach clearly is not working," he told Newshub.
The Drug Foundation says synthetic cannabis appears to be replacing the use of natural cannabis, with usage down by 20 percent.
Many police detainees say there is a cannabis drought, especially in the South Island, with the drug now much harder to come by.