Long-Term Cannabis Use and Cognitive Function: Findings from a Longitudinal Study

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A recently published study examined the effects of cannabis use on age-related cognitive function in adults. Noting the limited number of studies in this area compared to studies on cannabis use and short-term cognition, the researchers sought to examine the relationship between cannabis use from early adulthood to late midlife and cognitive decline. The study, “Cannabis Use and Age-Related Changes in Cognitive Function From Early Adulthood to Late Midlife in 5162 Danish Men,” was published in November 2024 in Brain and Behavior.

This study examined data from 5162 Danish men born between 1949-1961 who had participated in assessments on cognitive aging and in follow-up questionnaires. Data from the Danish Aging and Cognition (DanACo) cohort was used, which was administered when the mean age of the participants was 20. The follow up questionnaires covered socioeconomic, lifestyle, and health-related factors and was administered when the mean age of the participants was 64.

The follow-up examination asked about cannabis use and age of first cannabis use. Participants were categorized as either cannabis users or non-cannabis users based on frequency of use. Age of initiation to cannabis was categorized into less than 18 years of age, between ages 18-25, or older than 25 years of age.

In this study, cognitive decline was defined as the difference in IQ between early adulthood and late midlife.

Covariates included were years of education and training, years of weekly extreme binge drinking, psychiatric and somatic morbidity, smoking, and use of drugs other than cannabis, such as amphetamine.

Some of the findings noted in the results section of the study included:

• The mean cognitive decline was 6.2 IQ points for the whole study population over an average of 44 years.
• 39.3% had used cannabis at least once. The initiation age for most cannabis users (51.1%) was before 18.
• At the initial assessment, cannabis users had a slightly higher average IQ, while at the follow up assessment, the mean IQ difference between cannabis users and nonusers was somewhat larger.
• The population of cannabis users had a higher proportion of smokers, more years of binge drinking, and a significantly higher proportion with a history drug use.
• A higher proportion of cannabis users had previous hospital diagnoses with psychiatric disorders.

Additionally, there was less cognitive decline in cannabis users versus non-cannabis users: in the adjusted model, cannabis use was associated with 1.3 IQ points less cognitive decline. The researchers noted that this difference is modest may not have clinical significance.

Ultimately, the study concluded that, “Men with a history of cannabis use had less cognitive decline from early adulthood to late midlife compared to men without a history of cannabis use. Among cannabis users, neither age of initiation of cannabis use nor frequent use was significantly associated with a greater age-related cognitive decline.”

Reference

1. Høeg KM.; Frodegaard RL.; Grønkjær M.; Osler, M.; Mortensen, EL.; Flensborg-Madsen, T.; Okholm, GT. Cannabis Use and Age-Related Changes in Cognitive Function From Early Adulthood to Late Midlife in 5162 Danish Men. Brain Behav. (2024). doi:10.1002/brb3.70136