Young people who are heavy users of cannabis, amphetamines and alcohol risk having the ageing brains of 80-year-olds, increasing their risk of stroke and dementia, according to experts.
Researchers say there is growing evidence of brain damage, including premature ageing, memory problems and reduced intellect.
A New Zealand study this week pointed to reduced IQ in long-term cannabis users and a recent University of WA study suggests heavy drinking affects memory, not just of recent events but prospective or "future memory".
Royal Perth Hospital and UWA professor of emergency medicine Daniel Fatovich said brain scans of Perth amphetamine users, mostly aged in their 20s, had shown one in five had a lesion.
"Brain lesions are a part of normal ageing so if you're in your 80s, more than 90 per cent of people have the lesions, if you're in your 60s about 20 per cent of people have them, and if you're about 30 only 0.5 per cent will have them," he said.
"But in our study it was 17 per cent, which is obviously much higher than you would expect in that young age group.
"You see photos of people who've aged terribly after using amphetamines for a few years but we're forming the view that not only is it ageing you on the outside, it's ageing you on the inside."
Professor Fatovich said amphetamines appeared to affect the generation of new brain cells, either by stopping or impairing growth.
The brain's hippocampus, responsible for memory, was shown in studies to be smaller in amphetamine users. Heavy alcohol use appeared to have the same effect.
Alcohol and cannabis also impaired "pruning" which occurred in adolescence as millions of the brain's pathways were pared down to make it more efficient.
"It's an evolving issue but the analogy I give is that most people have an elderly grandparent and they're living and walking and talking, but for many of them they're not quite as sharp as they used to be," Professor Fatovich said.
"But maybe for people using these substances you're pushing that forward to a much younger age."
Professor Steve Allsop, of the National Drug Research Institute, said brain research was in its early stages but it suggested drug use had potential long-term effects.
"It impairs your performance now and the evidence is telling us there may be brain changes which affect you for life," he said.
Some effects were subtle - "like getting a C+ instead of a B+".