New figures from police wastewater drug testing reveal a spike in Aucklanders' MDMA use and a steady increase in cocaine use in the city.
Despite population differences, the results show drug use is largely more prevalent in Christchurch than it is in Auckland.
Wastewater testing began in Christchurch and Auckland in December last year, and a new testing operation in Whangarei started three months ago.
Data is collected from the wastewater facilities for one week every month and analysed for traces of methamphetamine, MDMA, or ecstasy, cocaine heroin and a-PVP.
The first three drugs were picked up in wastewater in all three of the testing spots. However, authorities overseeing the new pilot programme have so far failed to detect heroin and designer drug alpha-PVP.
The use of cocaine in Auckland was a stand-out increase, with the total grams detected per week having jumped from 36g in June, to 95g in November.
Commentary on the police report released today said there were "growing concerns" around the increase of methamphetamine and cocaine seen domestically.
The report also pulled observations about New Zealand's ecstasy market, based on MDMA levels.
"The level of MDMA detected has informed agencies that actual MDMA is present in
New Zealand's ecstasy market, though it is likely many analogues and substitutes are still used," it said.
Figures showed a significant increase in the use of MDMA across both sites over the past six months - and shockingly revealed use in Christchurch is nearly double that in Auckland.
A big increase in MDMA was detected in Christchurch, where 599g was detected in November versus 199g in June. Likewise, 265g of the drug showed up in Auckland's wastewater testing in November - up from 85g back in June.
Despite this, both regions saw big fluctuations in use of the drug month to month.
Use of methamphetamine was significantly up in Christchurch - from 640g in June to 708g in November.
Further north, high levels of methamphetamine were found in Whangarei's wastewater treatment plant.
Police said the programme, which was run in conjunction with the Institute of Environmental Science and Research, aimed to help better understand the geography of drug use.