Cannabis Users Have 20% or 1.3 IQ Points Less Cognitive Decline Over 44 Years
One recent study revealed the Endocannabinoid System‘s effect on Alzheimer’s Disease. Then this recent study suggests Stoners have less cognitive decline over time, something I’ve noticed as well as that I don’t know any with Alzheimer’s (yes, it’s only n=1, but still):
Cannabis Use and Age-Related Changes in Cognitive
Function From Early Adulthood to Late Midlife in 5,162
Danish Men
1 Introduction
Since the 1960s, cannabis use has been rapidly increasing,
especially among younger people, reaching its peak in the
late 1970s (World Health Organization; Committee on the
Health Effects of Marijuana: An Evidence Review and Research
Agenda, Board on Population Health and Public Health Practice,
Health and Medicine Division, National Academies of Sciences,
Engineering, and Medicine 2017).
Cannabis is currently classified under Schedule I of drugs by the United States Drug Enforcement Administration, which is a list including drugs with no currently accepted medical use and a high potential for abuse (USC
Environmental Health & Safety). Recreational use of cannabis
is illegal in Denmark; however, according to a recent report from
the Danish Health Authority, 9.7% of the Danish population aged
16–44 use cannabis annually (Sundhedsstyrelsen 2022).
Given the high prevalence of cannabis use, its potential association with
cognitive decline could have significant implications for public
health. While there is substantial evidence of the short-term
negative effects of cannabis use on cognition and cognitive
development (Dellazizzo et al. 2022; Lubman, Cheetham, and
Yücel 2015; Lyketsos et al. 1999; Noorbakhsh et al. 2020), its link
to age-related cognitive decline has been sparsely studied and
has shown mixed results (Auer et al. 2016; Lorenzetti, Hoch, and
Hall 2020; Lubman, Cheetham, and Yücel 2015; Lyketsos et al.
1999; McKetin et al. 2016; Meier et al. 2012; Watson et al. 2023).
For example, in a New Zealand longitudinal study conducted by
Meier et al. (2012), frequent cannabis use was associated with
steeper cognitive decline over more than 20 years, a decline
that was more pronounced the greater the cannabis use (Meier
et al. 2012). This study further revealed that adolescent cannabis
users were particularly vulnerable to more substantial IQ decline
compared to those who initiated cannabis use in adulthood
(Meier et al. 2012). Similarly, in an American longitudinal study
by Auer et al. (2016), prior cannabis exposure was associated with
impaired verbal memory, although it did not appear to affect
other cognitive domains (Auer et al. 2016). Contrarily, Lyketsos
et al. (1999), in another American longitudinal study, found
no significant differences in cognitive decline between heavy
cannabis users, light users, and nonusers (Lyketsos et al. 1999).
This is consistent with findings from an Australian longitudinal
study by McKetin et al. (2016), which suggested that cannabis use
was not correlated with accelerated cognitive decline (McKetin
et al. 2016). Finally, in an American longitudinal study of older
adults with HIV by Watson et al. (2023), occasional cannabis users
demonstrated better overall cognitive performance compared to
nonusers, but the rates of cognitive decline and everyday function
did not vary according to the average cannabis use (Watson
et al. 2023).
The present study aimed to investigate the association between
cannabis use and age-related cognitive decline from early adulthood
to late midlife in a population of 5,162 men. In addition, we
aimed to investigate whether this association depended on age
of initiation of cannabis use and the number of years of frequent
cannabis use.
4 Discussion
4.1 Main Findings
In this study of 5,162 Danish men, the mean cognitive decline
was found to be 6.2 IQ points over an average of 44 years.
Notably, cannabis users exhibited statistically significantly less
cognitive decline compared to nonusers. In the fully adjusted
model, cannabis use was associated with 1.3 IQ points less
cognitive decline than the decline observed in the reference
group. However, the estimated difference in cognitive decline
between cannabis users and nonusers was modest (corresponding to 7% of a standard deviation) and may not hold clinical significance.
Among cannabis users, no significant associations with
age-related cognitive decline could be demonstrated for age of
initiation of cannabis use. Years of frequent cannabis use were
generally associated with no significant difference in cognitive
decline when compared with no frequent use.
4.2 Comparison With Previous Studies
Few studies with comparable long-term follow-up periods exist,
and most found no differences in cognitive decline between
cannabis users and nonusers. However, the limited studies on
this topic employed different methods than those utilized in the
present study, making direct comparisons less straightforward.
However, our findings do align with results from previous studies
indicating no greater age-related cognitive decline associated with
cannabis use. In an Australian longitudinal study, 1897 men and
women aged 40–46 were followed over 8 years, and it was found
that cannabis use was not associated with accelerated cognitive
decline in middle-aged adults (McKetin et al. 2016). Similarly, an
American longitudinal study followed 1318 men and women aged
18–64 over 12 years, finding no differences in cognitive decline
between heavy users, light users, and nonusers of cannabis
(Lyketsos et al. 1999). Finally, in an American longitudinal
study of 297 older adults with HIV, occasional cannabis users
demonstrated better overall cognitive performance compared to
nonusers, although the rates of cognitive decline and everyday
function did not vary with the level of cannabis use (Watson et al.
2023).
The observed association of less cognitive decline among
cannabis users compared to nonusers in this study may reflect
characteristics of cannabis users rather than the direct effects of
cannabis itself. For example, cannabis users tended to have higher
baseline IQ and education levels, and they tended to smoke more
tobacco and consume more alcohol. Hence, it is reasonable to
assume that additional unmeasured factors might influence the
association, potentially confounding the result. Nevertheless, our
findings of less cognitive decline among cannabis users compared
to nonusers align with previous in vivo studies indicating that
cannabinoids have a positive impact on cognitive function and
memory in rats (Marchalant et al. 2008) and mice (Bilkei-Gorzo
et al. 2017; Sarne et al. 2018).
5 Conclusion
In the present study, we aimed to investigate the relationship
between cannabis use and age-related cognitive decline from
early adulthood to late midlife. 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. 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.
Read the study at: https://doi.org/10.1002/brb3.70136