New drug data shows a fall in the cost of methamphetamine seems to relate to increased consumption.

The New Zealand Drug Trends Survey reveals a gram cost about $334 last year - compared to $563 in 2017. 

Over the same period, the proportion of respondents using the drug every week rose from 27 percent to 57.

Massey University drug researcher Chris Wilkins says that like with any commodity, people will consume more when the price is down. 

"It seems that it's just current users that are using more because the price is cheaper."

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