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The lifetime use of cannabis was not associated with cognitive decline, according to a study of more than 5,000 men by Danish researchers. The study found that participants with a history of cannabis use experienced “significantly less cognitive decline” over their lifetimes than non-users, a finding that contradicts common stereotypes about the plant and people who use it.
The research, which was published this month in the peer-reviewed journal Brain and Behavior, followed 5,162 Danish men over several decades (a mean of 44 years). Participants’ IQ scores were assessed in early adulthood (mean age 22 years) and again later in life (mean age 62). The research also included extensive data on the health and lifestyle of the participants collected from follow-up questionnaires. The researchers then investigated the association between cannabis use and age-related cognitive decline using linear regression models.
The study found that participants with a history of cannabis use exhibited “significantly less cognitive decline” over their lifetimes than non-users. The research also determined that among participants who used cannabis, neither the age at which they began using cannabis nor their frequency of use was associated with negative cognitive effects.
The researchers determined that the mean cognitive decline among all participants was 6.2 IQ points over an average of 44 years. After adjusting confounding factors, “cannabis use was associated with 1.3 IQ points less cognitive decline than the decline observed in the reference group.”
“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,” the researchers reported in their results from the study. “Among cannabis users, neither age of initiation of cannabis use nor frequent use was significantly associated with a greater age-related cognitive decline.”
Findings Align with Other Research
The authors of the study concluded that their findings “align with most existing studies, suggesting no association between cannabis use and greater cognitive decline,” cannabis policy group the National Organization for the Reform of Marijuana Laws (NORML) noted in a report on the study.
“Among cannabis users, no significant associations with age-related cognitive decline could be demonstrated for age of initiation of cannabis use,” the researchers wrote. “Years of frequent cannabis use were generally associated with no significant difference in cognitive decline when compared with no frequent use. … 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.”
The results of the study are consistent with previous research into the effects of cannabis on cognitive decline. A recent review of research on the subject published in JAMA Psychiatry found little evidence that cannabis use has long-term effects on cognition.
“Associations between cannabis use and cognitive functioning in cross-sectional studies of adolescents and young adults are small and may be of questionable clinical importance for most individuals,” the authors wrote. “Furthermore, abstinence of longer than 72 hours diminishes cognitive deficits associated with cannabis use.”
Paul Armentano, NORML deputy director, noted that the findings challenge a commonly held belief.
“These results contradict one of the more prominent and longstanding stereotypes about cannabis and cannabis consumers,” Armentano said in a statement from the advocacy group. “It is unfortunate that these stereotypes often go unchallenged in the media and elsewhere. It is even more unfortunate that studies refuting these long-held stereotypes seldom receive the type of mainstream attention they deserve.”
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