Medical cannabis and cognition

A new Victorian study has made significant findings in the use of medical cannabis, suggesting that when used as prescribed to manage a chronic health condition, cannabis does not negatively impact cognitive function.

It was conducted by researchers at Swinburne University of Technology’s Centre for Human Psychopharmacology. 

Previous studies into the acute effects of cannabis on cognitive function have typically involved young, healthy volunteers, while the average age of a medical cannabis patient in Australia is approximately 45-55 years.  

And given the age-related changes in cognitive function and age-related differences in the effects of cannabis on cognitive function, the authors highlighted that this age differential has complicated the generalisation of findings from non-medical cannabis studies to patient populations. 

Lead researcher, Dr Thomas Arkell, explained that with increasing medical cannabis use in Australia and other international jurisdictions, there was considerable interest in the development of novel methods that might allow patients to assess their cognitive function in relation to their own baseline before performing safety-sensitive tasks such as driving, 

“We already know that non-medical cannabis can impact memory and attention. However, our findings show that patients prescribed medical cannabis by a doctor don’t experience the same effects,” Dr Arkell said. 

“It could also mean that patients experience some alleviation of their symptoms, such as pain, after using medical cannabis, which might lead to a normalisation of cognitive function.” 

The research focused on patients taking a stable dose of medical cannabis and found that they might become tolerant to the potentially impairing effects of delta-9-tetrahydrocannabinol (THC), the primary psychoactive component. 

Participants were patients aged under 21 years; in possession of an unrestricted driver’s licence; had been prescribed any medical cannabis product to manage a refractory health condition; could undertake a seven-hour session without using medical cannabis more than once; and were confident using a product containing ≥ 1 mg THC per dose. 

Chronic non-cancer pain was the most common indication for medical cannabis use, followed by sleep disorders and anxiety, and most participants had been using medical cannabis for more than 30 days at the time of their registration into the trial.  

Participants reported the subjective drug effects over time, with post hoc tests revealing that participants who self-administered flower-based product rated themselves as significantly more stoned relative to baseline at 1 hour, 2 hours and 4 hours, while participants who self-administered oil rated themselves as significantly more stoned relative to baseline at 2 and 4 hours, but not at one. 

The team from Swinburne found that there was a significant main effect of time on median reaction latency and multitasking, but no effect of product type or a time/product type interaction for either outcome. 

Similarly, the main effects of time and product type on both outcome measures for pattern recognition memory were non-significant, as were all four outcome measures for reaction time and spatial working memory. 

“This could indicate that patients develop tolerance over time, akin to what we see with other psychoactive medications like antidepressants and benzodiazepines,” Dr Arkell explained. 

“And while this research marks a critical step in understanding the impact of prescribed medical cannabis on cognitive function, the results cannot be generalised to non-medical cannabis or non-prescribed medical cannabis use. 

“This was only a small study and further research is needed. However, these findings have real implications for the many thousands of Australians who are now prescribed medical cannabis to manage a chronic health condition.” 

All patients reported daily use of medical cannabis and a mean improvement in their condition of 78.59% since commencing treatment.