Medical cannabis use improves executive function in adults, according to emerging research further supported by recent (2021) preliminary results published in the Journal of the International Neuropsychological Society by Kelly Sagar and colleagues.

Executive function is the ability to think clearly and effectively.  It develops in late childhood and in the teenage years but may not be complete in some individuals until their mid-twenties.  Executive function is often discussed in terms of working memory, cognitive flexibility, and inhibitory control.  Aspects of executive function are measured by sets of well-known and widely validated tests, including such tests as the Stroop Color Word Test, the Trial Making Test, the Wisconsin Card Sorting Test, and the Rey Auditory Visual Test.

There are many studies that find a relation between early onset of cannabis use with poor cognitive performance.  One casual hypothesis is that heavy THC exposure impairs ongoing neurodevelopment in users.  Nonetheless, research findings on the impact of medical cannabis (MC) use on cognition are not consistent with these findings on early onset users.  

Sagar and colleagues point to recent results from a study that “examined the short-term effects of THC in MC patients at baseline (not intoxicated), immediately after using high THC (20%) cannabis products, and several hours later. Although the authors hypothesized poorer performance during intoxication, findings revealed stable or improved performance across several cognitive domains.” 

The authors note that “It is possible that if MC treatment reduces physical or psychological symptoms, cognitive function may actually improve as patients feel better.”   Pain, poor sleep, and anxiety have been shown to affect cognition and executive function.

The current study examines 54 medical cannabis patients that completed at least one of three test sessions, at 3 months, 6 months, and 12 months after a period of medical cannabis use.  The patients were relatively new to cannabis use, either cannabis-naïve or having not used it in the last 12 months prior to their medical cannabis use.  Medical cannabis was used for a variety of symptoms, including pain anxiety, PTSD, sleep, mood, and anxiety.  The subjects had used medical cannabis 9 to 11 times a week.

Tests were administered to measure executive function, verbal learning, clinical changes, and sleep.  In the area of executive functioning, subjects scored higher on the Stroop Color Word Test, faster on the Trail Making Test, and improved on other executive function tests such as the Letter Number Sequencing Test from the Weschler Adult Intelligence Scale-Revisited.  In the area of verbal learning, memory skills were maintained.

The clinical changes show improvements in mood and a reduction in anxiety, along with better sleep.  Subjects had decreased mood disturbance scores at each successive test, as well as reductions in self-reported depression and anxiety.   Sleep quality also improved.

While considered preliminary results, due to limitations on the study design, these findings support the study’s hypothesis that medical cannabis use does not cause cognitive decline.  The executive function improvement was not correlated with THC consumption, however data collected on cannabidiol (CBD) consumption suggests a pathway for the improvements in executive function.  CBD is correlated with better mood and less anxiety, which contributes to better sleep and an overall improvement in well-being.

These preliminary findings provide support for observing “inherent differences” between recreational and medical cannabis users, even while these subpopulations overlap in terms of onset of and prior use of cannabis.  Many recreational users seek high potency levels of THC, as do many medical users.  “However, [medical users] often want to avoid feeling intoxicated, and frequently seek products with varied cannabinoid profiles, particularly those containing cannabidiol (CBD), a non-intoxicating cannabinoid touted for its therapeutic potential. “  

This was a 12-month longitudinal, observational study.  Patients using medical cannabis for various conditions “exhibited improved executive function and stable learning and memory within the context of improvements on measures of mood, anxiety, and sleep relative to baseline.”  The clinical state of the patients improved over time and was associated with CBD exposure.  As to additional research, “examining the impact of individual cannabinoids and age of onset of use are warranted to clarify the implications of MC use.”

Sagar, Kelly A.; Dahlgren, M. Kathryn; Lambros, Ashley M.; Smith, Rosemary T.; El-Abboud, Celine; Gruber, Staci A. (2021) An Observational, Longitudinal Study of Cognition in Medical Cannabis Patients over the Course of 12 Months of Treatment: Preliminary Results.  Journal of the International Neuropsychological Society.  Vol. 27 Issue 6, p648-660.