While cocaine and ecstasy are popular on weekends, Auckland meth users appear to indulge every day of the week.
Using samples from the city's wastewater treatment plants, researchers found "high levels of methamphetamine, codeine, morphine and methadone", while cocaine and MDMA - the active ingredient in ecstasy - were "relatively rare".
While meth consumption was high every day, ecstasy spiked at weekends. Cocaine also only showed up at weekends, but only in one of the two plants samples were taken from.
"An overall mean of 360mg of methamphetamine and 60mg of MDMA was estimated to have been consumed per day per 1000 people," the study notes.
That's almost half a kilogram of meth across Auckland, on average, every day.
Meth's popularity during the week is "indicative of its addictive status and use as a stimulant in work activities", the University of Queensland and Massey University researchers claim.
"Amphetamine and methamphetamine were detected fairly consistently across the days of the week, suggesting that use is not limited to late-night weekend partying.
"The stimulant properties of methamphetamine have long been known to have utility for a range of work activities which require long periods of stamina and concentration, including truck driving, construction, hospitality and housework."
JHW-018, a banned synthetic cannabinoid found in former "legal high" products, was detected once. Ketamine ('special K') and mephedrone ('meow meow') weren't detected at all.
The researchers note the low detection rate of MDMA suggests much of what's sold on the streets as 'ecstasy' isn't the real thing.
"Previous national drug surveys and drug monitoring studies have suggested higher levels of 'ecstasy' use and availability than cocaine in New Zealand, but these questions refer to the street term 'ecstasy' rather the specific chemical compound, MDMA, which is detected in the wastewater analysis," the study reads.
"It is known that the global supply of MDMA was greatly disrupted after 2008, and this resulted in the use of a range of substitute compounds in 'ecstasy' such as methylone and methylethcathinone."
Marijuana was not tested for in the study, due to budget constraints.
It's the first time wastewater has been analysed for evidence of drug use in New Zealand, and follows similar research in North America, Asia and Australia. The samples were taken between May and July 2014.
The study was published on Monday in journal Drug and Alcohol Review.