Naturalistic investigation of cannabis strains varying in THC and CBD ratios and verbal recognition memory

Cannabis, which contains cannabinoids delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), has become the third-most-commonly used psychoactive substance in the United States. The legal market has grown alongside the increase in adult cannabis use, resulting in greater availability of products with a wide range of THC and CBD content. One of the most consistently observed cognitive effects of cannabis use is impairment of verbal memory. Although previous research shows that THC reduces accuracy in verbal memory tasks, less is known about potential differential acute effects of THC and CBD on recognition memory. Previous studies have suggested a protective effect of CBD (when combined with THC) on recognition memory, though research is mixed.

In the current study, we hypothesized that THC would result in lower recognition memory accuracy, and that when paired with CBD, the CBD would reduce the effects of THC on memory. Participants were randomly assigned to one of three legal market strains of flower product with varying THC:CBD ratios: a THC-dominant strain (N = 40); a roughly 1:1 THC:CBD strain (N = 38); and a CBD-dominant strain (N = 38). Participants completed two experimental sessions in which they either (a) used their assigned strain ad libitum in their private residence, or (b) did not use cannabis prior to completing a recognition memory task in our mobile laboratory.

We found that participants assigned to the THC-based strain in the cannabis use condition demonstrated lower recognition memory accuracy, more false alarms, a more liberal response bias, and slower reaction time. In contrast, participants assigned to the 1:1 THC:CBD strain had no significant recognition memory impairment, supporting our hypothesis that CBD may reduce the effects of THC on memory.

Given that adult cannabis use has become more prevalent, our results have implications to public health. For individuals who use primarily THC-based products, strains that also contain CBD may hold harm reduction potential, as CBD could help mitigate the impact of THC on recognition memory. Notably, bodily sensations of intoxication did not differ significantly between THC-dominant strains with varying amounts of CBD.