Cannabis causes chaos in the brain as nerve activity becomes uncoordinated and inaccurate, a study has found.
The results may help explain links between cannabis and schizophrenia, scientists believe.
Researchers at the University of Bristol measured the brain responses of rats given a drug that mimics the psychoactive ingredient in cannabis.
They found that the drug completely disrupted co-ordinated brain waves across the hippocampus and prefrontal cortex.
The first brain region plays a key role in the formation of memories. The second is essential to planning, decision making and social behaviour. Both are heavily implicated in schizophrenia.
Rats exposed to the cannabis-like drug became unable to make accurate decisions when navigating through a maze.
The research is reported today in the Journal of Neuroscience.
Study leader Dr Matt Jones said: "Marijuana abuse is common among sufferers of schizophrenia and recent studies have shown that the psychoactive ingredient of marijuana can induce some symptoms of schizophrenia in healthy volunteers.
"These findings are therefore important for our understanding of psychiatric diseases, which may arise as a consequence of 'disorchestrated brains' and could be treated by retuning brain activity."
Co-author Michal Kucewicz, also from the University of Bristol, said: "These results are an important step forward in our understanding of how rhythmic activity in the brain underlies thought processes in health and disease."
The research was part of a Medical Research Council-funded collaboration between the university and drug company Eli Lilly & Co.