Less than a year since Adelaide was declared the nation's "ice capital", methamphetamine use in South Australia has fallen dramatically, according to a new study.

Key points: Adelaide meth data reveals about 40 hits per 1,000 people a day

Adelaide meth data reveals about 40 hits per 1,000 people a day That is significantly less than December 2017, when the city was declared the nation's ice capital

That is significantly less than December 2017, when the city was declared the nation's ice capital Use of other drugs including oxycodone and fentanyl has increased

The Australian Criminal Intelligence Commission (ACIC) today released its latest National Wastewater Drug Monitoring Program report.

Sewage analysis revealed the Northern Territory had the highest average capital city consumption of methylamphetamine nationally in April 2018.

According to the research, wastewater testing at four sites in Adelaide revealed about 40 doses of methamphetamine a day per 1,000 people — less than half the recent high of more than 90 doses per day.

"The sudden drop-off in use of methylamphetamine use in South Australia was striking," the report stated.

"Both in Western Australia and South Australia, consumption declined dramatically after December 2017. These were the states where use was historically highest in the nation.

"The recent declines in methylamphetamine use in South Australia and Western Australia are clear reversals in longer-term trends."

According to Michael Phelan, ACIC chief executive, about 1,005 kilograms of methamphetamine is consumed in South Australia each year.

"As well as 108.8kg of cocaine, 58.7kg of MDMA and 38.6kg of heroin," he said.

The total methamphetamine consumption for the state was lower in the Northern Territory.

"We estimate that 65.5kg of methylamphetamine is consumed in the Northern Territory each year, as well as 19.5kg of cocaine, 38.2kg of MDMA and 1.1kg of heroin," Mr Phelan said.

Yesterday, SA Police busted what they described as "one of the largest" meth labs ever discovered in the state at Morphett Vale and seized 120kg of powder and 11kg believed to be crystal meth.

Inside a Morphett Vale home where 120kg of powder were seized. ( Supplied: SAPOL )

University of South Australia Professor Jason White, who carried out some of the latest research, attributed the drop in meth use to a crackdown on suppliers.

"For a sudden change like that to occur, it would be almost certainly due to reduced availability of methamphetamine on the market," he told the ABC.

"There have been some significant intercepts in recent months and it's most likely that has reduced supply."

But Professor White said it was important to exercise caution.

"That's only one record from April this year so we're yet to see if that's sustained over a longer period of time," he said.

Rising use of cocaine, fentanyl and oxycodone

The ACIC report found rising levels of consumption in South Australia of the amphetamine MDA and oxycodone.

It also reported "unusually high" levels of fentanyl use in regional South Australia.

Professor White said those rises should be understood in the context of broader trends.

"MDA — there is a slight increase but we're lower than the national average. Oxycodone in South Australia [has] increased a bit but we're still lower than we were approximately two years ago," he said.

"Fentanyl in South Australia dropped and there is a little bit of an increase back up again, so those are not indicative of longer-term upward trends.

"[But] we need to keep an eye on the cocaine level, there is something of an upward trend off a relatively-low level in South Australia."

Adelaide's reputation as the nation's ice capital was established in December 2017, when a previous wastewater report showed ice use was significantly higher than the national average.

An ACIC report released last month which outlined drug trends found that methamphetamine bulk prices in 2016-17 were cheaper in South Australia than in any other state.

The cost of a kilogram of crystal meth in South Australia was as low as $50,000, up to $30,000 cheaper than in New South Wales and Victoria.