Sydneysiders are drinking less alcohol but using more cocaine, methylamphetamine and nicotine, as the nation spent more than $11 billion on illicit drugs last year.

The Australian Criminal Intelligence Commission has released its ninth snapshot of Australia's wastewater, revealing 11.5 tonnes of methylamphetamine was consumed nationwide last year, as well as 4.6 tonnes of cocaine, 2.2 tonnes of MDMA, and more than 900 kilograms of heroin.

Last year Australia consumed 4.6 tonnes of cocaine. Credit:Shutterstock

Of the $11.3 billion spent on illicit substances in the year to August 2019, of which $8.63 billion was spent on methylamphetamine.

"This is one of the more tragic, harmful and wasteful aspects of illicit drug markets: expenditure on drug purchases which might otherwise have been spent in the legitimate economy that generates illicit profits for the sole benefit of organised crime groups," said ACIC chief executive Michael Phelan.