Methamphetamine use in Perth has fallen according to a new study, but along with regional WA is still above the national average.
Results of a national study of wastewater found Perth no longer had the unwanted crown as the nation's meth capital, with its daily use of the drug ice falling to 42 doses per 1000 people in February from nearly 80 last October.
However, WA is still the state with the highest level of ice use.
"It looks like meth consumption is going down, the problem for us is we never knew why it was so high in the first place and now we don't know why it's going down," WA Police Commissioner Karl O'Callaghan told 6PR radio Thursday.
There has also been a five per cent fall in the crime rate in the 2016-17 financial year.
"The crime rate has been cascading downwards for about 18 months now, and we're about 12,000 offences down on last year, so at the same time the meth usage has gone down crime has gone down," he said.