There is some evidence to suggest that stoned subjects exhibit increased risk-taking and impaired decision-making, and score worse on memory tasks—and residual impairments have been detected days or even weeks after use. Some studies also link years of regular marijuana use to deficits in memory, learning, and concentration. A recent and widely discussed report on the IQs of New Zealanders followed since birth found that cannabis users who’d started their habit in adolescence had lower IQs than non-users.
- In this study, led by researchers at Duke University, “you could clearly see as a consequence of cannabis use, IQ goes down,” said Derik Hermann, a clinical neuroscientist at the Central Institute of Mental Health in Germany who was not involved in the research.
But not 4 months later, a re-analysis and computer simulation at the Ragnar Frisch Center for Economic Research in Oslo countered the Duke findings. Ole Rogeberg contended that socioeconomic factors, not marijuana use, contributed to the lower IQs seen in cannabis users.
- Rogeberg’s conclusion counters a sizeable literature, however, which supports a link between pot use and neurophysiological decline. Studies in both humans and animals suggest that people who acquiring a marijuana habit in adolescence face long-term negative impacts on brain function, with some users finding it difficult to concentrate and learn new tasks.
Notably, most studies on the subject suggest that while there may be negative consequences of smoking as a teen, users who begin in adulthood are generally unaffected. This may be due to endocannabinoid-directed reorganization of the brain during puberty, Hermann explained. The intake of cannabinoids that comes with pot use may cause irreversible “misleading of the neural growth,” he said.
In addition to the consequences for intelligence, many studies suggest that smoking marijuana raises the risk of schizophrenia, and may have similar effects on the brain. Hermann’s group used MRI to detect cannabis-associated neuron damage in the pre-frontal cortex and found that it was similar to brain changes seen in schizophrenia patients. Other studies further suggest that weed-smoking schizophrenics have greater disease-associated brain changes and perform worse on cognitive tests than their non-smoking counterparts.
Resourse: The Scientist