A new study on long-term cannabis use suggests the drug can cause significant brain abnormalities, affecting the memory and emotional processing.

The study by researchers at the Universities of Melbourne and Wollongong says the effects can be equivalent to those experienced by people with a mild traumatic brain injury.

They say the study also documents for the first time, that long term marijuana use affects all users, not just high risk categories such as the young and those susceptible to mental illness.

The chief executive of Melbourne's Odyssey House, Stefan Gruenert, says he is not surprised by the findings.

"If you're using cannabis daily, heavily and over a long period of time, the people in this study had been using for about ten years, then you are likely to have changes in the brain that are likely to lead to or mimic some of the symptoms of things like paranoia, memory loss, confusion," he said.

Mr Gruenert says the findings should serve as a warning about all long-term drug use.

"Anything used in heavy dose inappropriately for a long term can lead to damage," he said.

"I think this is another piece of information for us as a society to make us stop and think about whether legalising any of our current illicit drugs is a wise idea."