Dim and demented under the influence of cannabis

By Dr. Ananya Mandal, MDJun 10 2010

Dr Ananya Mandal, MD

New research shows what many Cannabis users have suspected or known for a while, continuous use can lead to dimmer brains. Australia ranks among the world's highest cannabis users and this puts the population at a high risk of developing dementia say researchers.

The study conducted by researchers at the University of Wollongong says that the brain comes back to its original state once the drug is withdrawn but the main psycho-active ingredient in cannabis, Tetrahydrocannabinol or THC, can stay in the body for long periods of time. In frequent users the levels of THC remain high and that can damage the brain in a more permanent way. Under the lingering influence of THC simple tasks may seem difficult says University of Wollongong clinical psychologist Robert Battista. “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 explained.

He said that he tested users and non users of the drug in memory, inhibition and attention related tests. He says long-term cannabis users surprisingly performed better at some tasks than newer users. “During the process of the brain reorganizing 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…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.',” he said.

But Curtin University National Drug Research Institute professor, Simon Lenton warns the results should not make cannabis users feel that the drug is a soft drug. “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…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,” he said. He enthused that that harmful effects of the drug is being understood by the population at large since cannabis use has been declining in Australia since the mid 1990s.