The abnormalities can cause psychotic symptoms and memory loss, the University of Melbourne said Tuesday in a news release.
Researchers at the University of Melbourne and the University of Wollongong used brain imaging to show the hippocampus and the amygdala, which regulate memory and emotional processing, were significantly reduced.
"These findings challenge the widespread perception of cannabis as having limited or no harmful effects on brain and behavior," said Dan Lubman, an addiction medicine specialist at Orygen Youth Health.
The study found long-term cannabis users had advanced their memory loss by about 15 years. The study authors said the memory loss could be likened to the damage suffered by patients with mild traumatic brain injury.