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The medical use of cannabis improved mental performance in a study from the USA. The elaborate study with 22 patients was conducted in the USA. The scientists used a test - the so-called MSIT test - which measures certain aspects of mental performance. During the test, functional magnetic resonance imaging was performed to measure brain activity during the test. The participants were examined before starting cannabis treatment and 3 months later.
After 3 months of cannabis treatment, patients showed improved performance on the MSIT, accompanied by changes in brain activity within specific brain regions. Cannabis improved both test reaction times and response accuracy. The authors wrote that after cannabis treatment, "patterns of brain activation more closely resembled those of healthy controls from previous studies than those before treatment, suggesting a possible normalisation of brain function compared to baseline." Study participants also reported health improvements, with improvements in pain, mood, quality of life and sleep.
Only people who had never used cannabis before or had not used cannabis for at least two years were allowed to participate in the study. They were on average 51 years old and suffered from pain (13 participants), anxiety or post-traumatic stress disorder (10), sleep disorders (10) and other symptoms.
The researchers pointed out that improvements in disease symptoms from cannabis could be directly responsible for the observed improvements in mental performance and changes in brain activation. For example, pain and anxiety are known to be associated with reduced mental performance. Therefore, a reduction in such symptoms could have directly led to cognitive improvements with positive effects on brain activity.
Another reason could be the reduction of common medications during the 3-month therapy with cannabis, including opiates, sleeping pills and antidepressants. The scientists wrote in their article that the reduced intake or complete discontinuation of conventional drugs could have caused the changes in brain activation. Several studies have shown that benzodiazepines, antidepressants and other psychiatric drugs can reduce brain activity.
Previous studies that had investigated the relationship between cannabis use and mental performance had invariably focused on recreational use of the drug. These generally found a reduction in mental performance and atypical brain activity. A number of factors may account for the difference between the results of the current study with patients and the earlier results with recreational users. For example, the majority of studies on recreational cannabis use have been conducted with adolescents and young adults. Since the participants in the current study were between 28 and 74 years old, their brain development had been completed for a long time and they were less sensitive to possible harm from THC than adolescents.
In addition, a study with mice from the Institute of Molecular Psychiatry at the University of Bonn was published in 2017, according to which THC could have the potential to improve mental performance in older animals. The older mice showed a reversal of age-related mental decline after administration of low doses of THC. The Bonn scientists suspected that this could be due to an activation of the ageing endocannabinoid system following THC administration. The same THC exposure led to a decrease in cognitive performance in young mice.
Another difference from previous studies is the strength of cannabis use. In the new study, patients used cannabis an average of 5 days a week and once or twice a day. Traditionally, studies with recreational users have examined chronic, heavy use.
The relationship between cannabis use and mental performance needs to be differentiated. The reason for use, the age of the user and the strength of cannabis use are important factors that modulate the effects on brain function. Sweeping claims that cannabis has a fundamentally negative effect on mental performance can no longer be upheld.