Mind altering effects of THC vs. CBD: Not what you may have thought!
Image from ©Lincoln Barbour
Recently, cannabis was legalized in Canada, and based on how many cannabis stores and cannabis products have sprung up, it seems there’s something for everyone! The more society becomes aware of chemicals in foods and drugs we consume, the more questions we have of the effects they have on our body and brain. A government led survey showed that the prevalence of cannabis use has increased among Canadians, with 27% of people reporting having used it in the past year, and people aged 16-24 years old reporting nearly double the cannabis use than those over 25 years. During the COVID-19 pandemic, an increase in cannabis use was seen in younger age groups, and the major reasons for the increase were boredom, anxiety, and stress. As the use of cannabis becomes more prominent in society, many questions arise about the effects it can have on our body and brain.
One of the most important factors that consumers typically consider when selecting what to buy in a cannabis shop is the balance of the chemical compounds, or phytocannabinoids. In particular, the balance of two particular molecules, THC (tetrahydrocannabinol) and CBD (cannabidiol), are important to consider. Studies have demonstrated that THC is the main psychoactive component that makes you feel ‘high’, while CBD is known for its calming and anti-psychotic effects, and some people even take it for conditions like anxiety and chronic pain.
When it came to choosing the relative THC and CBD levels in their products, 29% of the surveyed Canadians preferred higher THC content, while 25% did not know the levels of the these molecules in their products. Given that one of the main reasons Canadians use cannabis is to reduce anxiety and stress, are they really choosing the right balance of phytocannabinoids in their cannabis products to meet their needs?
To answer this question, we need to understand how the CBD and THC molecules affect the brain and behaviour. In a series of studies published in 2019 and 2021, Dr. Hanna Szkudlarek, PhD, and colleagues from Western University showed how THC and CBD have different effects on anxiety and cognition. To understand how these molecules affect behaviours, they conducted a series of behavioural and cognitive tasks in rats that were administered THC, CBD, THC + CBD, or saline as a control directly into the brain.
To study anxiety-related behaviours (something that many Canadians use cannabis to assist with), Dr. Szkudlarek measured the time it took for the rats to escape from an open space to a closed space. Rats are prey species, so they avoid open spaces and will prefer enclosed spaces and edges that could protect them from predators. Less time to escape from the open space is indicative of anxiety and panic-like behaviours. Dr. Szkudlarek in the 2021 study found that when only THC was administered, the time to escape the open space was much less than when CBD, CBD + THC, or saline were administered. This finding suggests that THC can cause panic-like behaviours, but this effect is taken away when CBD is also present.
Through these studies, Szkudlarek and colleagues also showed that CBD is not as non-psychoactive as we might have once thought! They conducted various tasks that tested how CBD and THC affected the rats’ ability to form fear-associated memories, show attentional flexibility, form working memories, and filter out irrelevant information.
To expand on these, fear-associated memories are formed when we go through a traumatic event, which causes us to fear the situational context that was associated with the event, for example, becoming scared of elevator music after a scary experience of being stuck on an elevator. In this study, fear-associated memories were formed through a fear conditioning task where the rat received a foot shock at the same time as playing a sound. This causes rats to associate that sound with a negative outcome (foot shock) and exhibit fear even when the sound is played without a foot shock. Formation of fear-associated memories are important as they allowed our ancestors to quickly learn to avoid harmful things and increased their chances of survival. Dr. Szkudlarek found that administering both CBD and CBD + THC impaired the rats’ ability to form these new fear-related memories, but not THC by itself.
Working memory helps us hold on to information for short periods of time and is important for decision making, like when we ask for directions and have to remember them long enough to reach our destination. In the next experiment, working memory was tested by letting the rats explore a maze and scoring how many times they returned to the same part of the maze. Typically, rats prefer to explore new areas, so if they keep returning to the same area it is indicative that they have impaired memory. With CBD administration the rats returned to the same area of the maze more often, meaning that CBD impaired the rats’ ability to form these short-term memories. When both THC and CBD were administered the rats explored the maze similarly to the control rats, meaning their memory was not impaired, indicating that THC may reverse some mind-altering effects of CBD as well.
Attentional flexibility measured how well the rats could change strategies when doing a cognitive task. Dr. Szkudlarek described it as a situation where you try to open the door to your office by pushing, but someone changed the door overnight so now you need to pull, and how long it takes you to realize that you need to pull instead of push is a measure of your attentional flexibility. Again, they found this function was impaired by CBD, but not when only THC or THC + CBD was given.
Finally, filtering out irrelevant sensory information from our environment is important for our everyday lives. For example, it helps us pay attention to a conversation in a noisy café by ignoring the irrelevant background noise. Sensory filtering was measured by allowing the rats to explore a space where 3 objects were placed, 2 identical and 1 slightly different, and the amount of time the rats spent by the different objects was measured. Similar to the previous test, rats prefer novelty and their preference for spending more time with the different object means they are able to filter out irrelevant information about the objects and recognize the different one. Dr. Szkudlarek found that CBD, but not THC or THC + CBD, caused the rats to not have a preference for the different object, meaning the rats’ ability to filter out irrelevant information was hindered.
The findings of these studies are surprising when you consider the “vast literature on detrimental effects of THC vs. beneficial actions of CBD,” according to Dr. Szkudlarek, since they found it was CBD, not THC, that impaired cognitive functions. They showed that CBD “can interfere with how the environment is perceived, [and] whether the irrelevant information can be successfully filtered out or how quickly new strategies to achieve the goal can be executed.” Interestingly, the co-presence of THC negated a lot of the adverse behavioural effects of CBD, and vice-versa. It is important to keep in mind that the brains of rodents and humans are different, and these findings may not perfectly translate to humans. However, there are also many similarities in molecular pathways in the brains of rodents and humans, which allows us to use rodent models to study human brain-related phenomena. Moreover, animal studies are important as they allow us to conduct experiments that would not be feasible in humans (e.g. injecting CBD or THC directly into the brain), and thus help us better understand certain topics.
So what strategies should people use when choosing the contents of their cannabis product? The first step is to become aware of the effects that THC and CBD can have on your brain and behaviour. Dr. Szkudlarek hopes these studies “highlight the importance of balancing THC/CBD during cannabis exposure to mitigate potential anxiogenic THC effects and cognitive CBD effects.” Finally, it is important to stay up to date on the ongoing research, which may be enlightening as the study of THC and CBD is still in its infancy and new scientific research may regularly change our understanding of this topic, so consumers can make the most informed decisions for themselves.