New research has found no association between long-term cannabis use and cognitive decline in later life.
Longitudinal data published in the journal Brain and Behavior, found no significant harmful effects of cannabis use on age-related cognitive decline.
Researchers in Denmark examined the relationship between lifetime cannabis use and age-related cognitive decline in a sample of over 5,000 men from the Danish Aging and Cognition (DanACo) cohort, which was designed to study predictors of age-related cognitive decline from young adulthood to late midlife.
Participants’ IQs were assessed during early adulthood (average age 22) and again in late midlife (average age 62).
Cognitive decline was defined as the difference in IQ between the two assessments of cognitive ability conducted in early adulthood and late midlife.
According to the results, those with a history of cannabis use exhibited “statistically significantly less cognitive decline” compared to non-users. However, the authors caution that the estimated difference in cognitive decline between cannabis users and non-users was modest and may not hold clinical significance.
Among cannabis consumers neither the age of initiation nor frequency of use was associated with negative effects on cognition. Over half (51.1%) of cannabis users began consuming before the age of 18 and with 43.5% beginning between the ages of 18 and 25, and just 5.4% after this.
The reduction in cognitive decline could be due to the characteristics of the participants rather than the effects of cannabis itself, for example, cannabis users tended to have higher baseline IQ and education levels, and tended to smoke more tobacco and consume more alcohol.
But the findings do align with previous studies which have suggested that cannabinoids could have a positive impact on cognitive function and memory in rats.
The authors conclude: “This study contributes to the sparse knowledge on this subject and aligns with most existing studies, suggesting no association between cannabis use and greater cognitive decline.
“More specifically, in the present study, cannabis users experienced slightly less cognitive decline compared to nonusers, and the association remained significant when controlling for potential confounders. Among cannabis users, no significant association was found with cognitive decline for either age of initiation of cannabis use or frequent cannabis use.”
They add: “Further studies are needed to investigate whether these findings reflect that there are no adverse effects on cognitive decline or that the effects of cannabis are temporary and disappear after a prolonged period of time.”