Friday 11 Jun 2010
New research shows how the brains of chronic cannabis users become less efficient than the brains of people who do not use the drug.
The University of Wollongong study also shows that over time the drug users' brains adapt and almost come back up to speed.
But experts say the study shows more evidence that cannabis should not be regarded as a soft drug.
The study shows the main psycho-active ingredient in cannabis, THC, lingers in the body for weeks, meaning that the brains of frequent users could be constantly exposed to the chemical.
University of Wollongong clinical psychologist Robert Battista says lingering effects of THC mean users' brains have to work harder to do the same tasks as people who do not use cannabis
"It is kind of like if you are driving your car down a freeway and the freeway is the most efficient neural pathway ... [cannabis users might find] the road has potholes or there is fog so that it is more effortful, more resources have to go into doing that same task," he said.
Mr Battista says for the study he asked cannabis users to perform tasks testing their memory, inhibition and attention.
He says long-term cannabis users surprisingly performed better at some tasks than newer users.
"During the process of the brain reorganising itself over an extended period of time, it looked like that long-term cannabis users were actually getting some recovery of their memory function with a longer history of use," he said.
"It is essentially the brain going: 'Okay, well these old pathways that we would prefer to use we can't because they have been disrupted so we'll have to use these other ones and we'll get better and better at using them.'"
But Curtin University National Drug Research Institute professor, Simon Lenton, says cannabis users should not get complacent.
He says many studies have been trying to establish if users can restore their cognitive functions over time.
"The picture is mixed. Some studies suggest that functioning does improve after a period of abstinence and for others ... it looks like it doesn't," he said.
"I think we are still at early days in terms of not only understanding the impact of cannabis on the brain, but also understanding the longer-term impacts and what happens when people stop using cannabis."
Professor Lenton says the new research is one of a number of studies to emerge over the past 10 years showing cognitive problems for chronic cannabis users.
He says the message does seem to be getting through that the drug is harmful, as cannabis use has been declining in Australia since the mid 1990s.