BRISBANE, Jan 12 - Better parental attitudes about the dangers have been linked to the trend, identified by an analysis of more than 40,000 student surveys completed in Victoria, Queensland and Western Australia between 1999 and 2015.
But so, too, has the fact it's become harder for kids to get their hands on harmful substances.
"Alcohol, tobacco and cannabis use all fell significantly from 1999 to 2015," Australian researchers found, but noted higher levels of use in Victoria compared to the other two states.
It said the reductions appeared to go hand-in-hand with less tolerant parental attitudes towards drugs, and the fact students had greater difficulty accessing them.
"It is plausible that a reduced tendency for parents and other adults to supply adolescent alcohol are implicated in the reductions in adolescent alcohol use observed across Australia," the study found.
The study is the work of researchers at Deakin University, the Murdoch Children's Research Institute, and the Alcohol and Drug Foundation, and has been published in the Drug and Alcohol Review journal.