Tags:  Chronic cannabis use; Neuropsychology; Memory; meta-analysis

 

The problem: We all know that cannabis has acute neurocognitive effects. However, we don’t know much about the cognitive effects of long-term use.

 

The study: The authors performed a thorough literature review to identify any links between chronic cannabis use and neurocognitive impairments. They searched scientific databases (e.g. PubMed, Ovid Medline) to identify studies published between 2010 and 2019 that described chronic cannabis use and neurocognitive function. Studies only included ongoing cannabis users who were 18 years or older. All studies compared cannabis users to people with no cannabis use.

 

Main results:

• 13 studies were included.

• There was a small but statistically significant (p<0.05) cross-sectional association between chronic cannabis use and cognitive impairment in the following functional domains: cognitive impulsivity, cognitive flexibility, attention, short-term memory and long-term memory.

• However, no association was found between chronic cannabis use and motor impulsivity.

 

Conclusions:  Chronic cannabis seems to reduce cognitive function in several ways, including attention and memory. 

 

Why this is a good study:

• The authors used rigorous methods to find published studies, so this is a pretty complete roundup of existing data

• They used sophisticated statistical methods to combine studies

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Why this isn’t a perfect study:

• The authors could take into account some other variables that affect thinking and memory, such as alcohol use, but they didn’t have access to a lot of data.

• This study couldn’t analyze the effect of dose.  Does cannabis impair thinking more is you use more frequently?  Or if you use for a longer period of time?  We don’t know.

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What this study adds:

• This study provides strong evidence that cannabis can impair memory, and points to impairments in other neurocognitive domains. 

• That effect is independent of at least some other factors, like alcohol use

• The overall effect is real, but probably pretty small. 

 

What it doesn’t:

• This is a study of neuropsychological tests, which are very sensitive.  An abnormal test doesn’t mean that someone would feel—or behave—any differently.  (Think of a lab test that might be a little higher than normal.  But you feel fine.   And you are fine—it’s just a number that’s a little off).

 

Funder:  No agency funding was reported.

 

Author conflicts:  None