Does medical cannabis really cause cognitive impairment?

This small study examined the cognitive effects of sustained medical cannabis use on patients during a single laboratory session. It was published in November 2023 in the journal CNS Drugs.

They used the Cambridge Neuropsychological Test Automated Battery (CANTAB) and Druid application to determine levels and changes in cognitive function before and after patients self-administered their standard dose of medical cannabis. 

The CANTAB tests included:

  • Multitasking Test (MTT)
  • Pattern Recognition Memory (PRM)
  • Reaction Time (RTI)
  • Rapid Visual Information Processing (RVP)
  • Spatial Span (SSP)
  • Spatial Working Memory (SWM)

"Together, these tests assess working memory, sustained attention, response time, impulsivity, pattern recognition memory, and executive function."

40 patients (22 female, 18 male) were included. The average age was 41, and they averaged 10 months of medical cannabis use before the study. 23 took oral cannabis oils and 17 vaporized cannabis flower. 

Chronic non-cancer pain was the most common reason for medical cannabis use (n = 20), followed by sleep disorder (n = 18) and anxiety (n = 11).

The average doses taken:

  • Oral Cannabis Oil: 9.6mg THC and 9.2mg CBD
  • Vaporized Flower: 37mg THC and 0.4mg CBD


One interesting result was that the participants actually improved on several tests AFTER taking medical cannabis. All other measured changes were not considered significant. Additionally those participants taking vaporized flower (higher THC dose without much CBD) felt much greater feelings of being "stoned" or sedated than those taking oral oils with a balanced THC/CBD ratio.

The authors' results and conclusions:

Participants’ performance improved over time on the CANTAB Multitasking Test and Rapid Visual Information Processing test

All other changes in cognitive performance measures over time were non-significant

Medical cannabis, when used as prescribed, did not negatively impact cognitive function.

This study provides preliminary evidence to suggest that medical cannabis may have minimal acute impact on cognitive function when prescribed and used as directed.


The full text article is here at PubMed Central.



Arkell TR, Manning B, Downey LA, Hayley AC. A Semi-Naturalistic, Open-Label Trial Examining the Effect of Prescribed Medical Cannabis on Neurocognitive Performance. CNS Drugs. 2023 Nov;37(11):981-992. doi: 10.1007/s40263-023-01046-z. Epub 2023 Nov 9. PMID: 37945917; PMCID: PMC10667416.