More than a quarter of middle-aged New Zealanders have tried methamphetamine at least once, according to a recently published study.
The University of Otago, Christchurch's Christchurch Health and Development Study has tracked more than 1000 people since their birth in in Canterbury in 1977.
Participants were asked during at ages 21, 25, 30 and 35 about methamphetamine use as well as involvement in violence, either as a victim or perpetrator.
The study, which was recently published in the Drug and Alcohol Dependence journal, found 28 percent of participants reported using the drug at least once between the age of 18 and 35, while 11 percent used it monthly at some point and 4.9 percent had used it weekly at some point.
Director of the Christchurch Health and Development Study Professor Joe Boden said the study also revealed the drug's link with violence.
"There's about a 60 percent increase in risk of violent assault - that's during a period when a person has reported using meth and told us that they had assaulted someone," he said.
"So that's actually a pretty sizeable increase.
"We quoted the figure of a population attributable fraction of 14 percent and what that basically means is that 14 percent of all violent assault that we observed in our cohort is due to meth. The analogue is basically if you removed meth you'd decrease the assault rate by 14 percent."
It marked the first time the use of methamphetamine and its links to violence had been studied in a longitudinal, or life course, research group, Prof Boden said.
International research and intelligence showed global drug supply networks originating in Asia had broadened their reach in the last decade and were now trafficking more pure crystalline forms of methamphetamine, which led to a greater burden of methamphetamine harms and the perception of harms, he said.
"It has long been suggested that amphetamines increase the risk of violence perpetration and victimization, but evidence thus far has shown only evidence of association, rather than a direct causal link."
Methamphetamine was the third most common illicit drug after cannabis and ecstasy, according to Christchurch Health and Development Study data.
"Some violence is likely associated with involvement in the drug trade, but our study findings indicate that reducing rates of methamphetamine use in the population overall would result in decreased incidence of violent assaults."
While methamphetamine use increased the risk of involvement in violence most people who used the drug did not engage in violence or experience violence in others, he said.