Researchers explore how cannabis affects cognition and psychology
EDITOR’S NOTE – In May 2021, Alabama Governor Kay Ivey signed into law a measure that allows people with a qualifying medical condition to purchase what is commonly referred to as medical marijuana. Medical marijuana, or medical cannabis, is derived from the Cannabis sativa plant, which has mood-altering chemical properties and is often used recreationally. Cannabis contains two compounds: THC, which makes people feel high, and CBD, which many believe has medicinal properties. As the discussion of these medical uses continues, this research article from The Conversation provides some interesting insights into the potential harms of prolonged marijuana use, especially by and for young people. The Alabama Baptist provides this information as a resource for our readers, and not as an endorsement of the researchers or any publication or website cited in the article.
Cannabis has been used by humans for thousands of years and is one of the most popular [recreational] drugs today. With effects such as feelings of joy and relaxation, it is also legal to prescribe or take in several countries.
But how does drug use affect the mind? In three recent studies, published in The Journal of Psychopharmacology, Neuropsychopharmacology and the International Journal of Neuropsychopharmacologywe show that it can influence a number of cognitive and psychological processes.
The United Nations Office on Drugs and Crime reported that in 2018, approximately 192 million people worldwide between the ages of 15 and 64 used cannabis recreationally. Young adults are particularly fond, with 35% of people between 18 and 25 use it, while only 10% of people over 26 do.
This indicates that the main users are teenagers and young adults, brains are still developing. They can therefore be particularly vulnerable to the effects of cannabis use on the brain in the longer term.
Tetrahydrocannabinol (THC) is the main psychoactive compound in cannabis. It acts on the “endocannabinoid system” of the brain, which are receptors that respond to the chemicals in cannabis. Cannabis receptors are densely populated in the prefrontal and limbic areas of the brain, which are involved in reward and motivation. They regulate the signaling of brain chemicals, dopamine, gamma-aminobutyric acid (GABA) and glutamate.
We know that dopamine is involved in motivation, reward, and learning. GABA and glutamate play a role in cognitive processes, including learning and memory.
Cannabis use can affect cognition, especially in people with cannabis use disorders. This is characterized by a persistent desire to use the drug and disruption of daily activities, such as work or education. It was estimated that approximately 10% of cannabis users meet the diagnostic criteria for this disorder.
In our research, we tested the cognition of 39 people with the disorder (who were asked to potty train on the day of the test) and compared it to that of 20 people who never or rarely used cannabis. . We showed that participants with the disease performed significantly worse on memory tests from the Cambridge Automated Neuropsychological Test Battery (CANTAB) compared to controls, who had never or very rarely used cannabis. It also negatively affected their “executive functions,” which are mental processes involving flexible thinking. This effect appears to be related to the age at which people started taking the drug – the younger they were, the more their executive functioning was impaired.
Cognitive impairments have also been observed in light cannabis users. These users tend to do riskier decisions than others and have more problems with planning.
Although most studies have been conducted on men, there are was the proof gender differences in the effects of cannabis use on cognition. We showed that while male cannabis users had poorer memory for visually recognizing things, female users had more problems with attention and executive functions. These sex-related effects persisted when controlling for age; IQ; alcohol and nicotine consumption; mood and anxiety symptoms; emotional stability; and impulsive behavior.
Reward, motivation and sanity
Cannabis use can also affect how we feel, further influencing how we think. For example, some previous research has suggested that reward and motivation—and the brain circuits involved in these processes— can be disturbed when we use cannabis. It can affect our performance in school or work, as it can make us less motivated to work hard and less rewarded when we do well.
In our recent study, we used a brain imaging task, in which participants were placed in a scanner and viewed orange or blue squares. The orange squares would lead to a monetary reward, after a delay, if the participant responded. This setup helped us study how the brain responds to rewards. We particularly focused on the ventral striatum, which is a key region of the brain’s reward system. We found that the effects on the reward system in the brain were subtle, with no direct effects of cannabis in the ventral striatum. However, the participants in our study were moderate cannabis users. Effects may be more pronounced in cannabis users with more severe and chronic use, as seen in cannabis use disorder.
There is also evidence that cannabis can lead to mental health issues. We have shown that it is linked to higher “anhedonia” – an inability to feel pleasure – in adolescents. Interestingly, this effect was particularly pronounced during the lockdowns related to the COVID-19 pandemic.
Cannabis use during adolescence has also been reported as a risk factor for developing psychotic experiences as well as schizophrenia. A study has shown that cannabis use moderately increases the risk of psychotic symptoms in young people, but that it has a much stronger effect in those with a predisposition to psychosis (scoring high on a checklist of symptoms of paranoid thinking and psychoticism).
Assessing 2,437 adolescents and young adults (14-24 years old), the authors reported a six percentage point increased risk – from 15% to 21% – of psychotic symptoms in cannabis users without a predisposition to psychosis. But there was a 26-point increase in the risk – from 25% to 51% – of psychotic symptoms in cannabis users prone to psychosis.
We don’t really know why cannabis is linked to psychotic episodes, but hypotheses suggest dopamine and glutamate can be important in the neurobiology of these conditions.
Another study of 780 adolescents suggested that the association between cannabis use and psychotic experiences was also linked to a region of the brain called the “uncus.” This is located in the Para hippocampus (involved in memory) and the olfactory bulb (involved in the processing of odors), and has a large number of cannabinoid receptors. It has also been previously associated with schizophrenia and psychotic experiences.
The cognitive and psychological effects of cannabis use are ultimately likely to depend to some degree on dosage (frequency, duration, and strength), gender, genetic vulnerabilities, and age of onset. But we need to determine whether these effects are temporary or permanent. An article summarizing numerous studies suggested that with light cannabis use, the effects may weaken after periods of abstinence.
But even if that’s the case, it’s clearly worth considering the effects prolonged cannabis use can have on our minds – especially for young people whose brains are still developing.
Barbara Jacquelyn Sahakianprofessor of clinical neuropsychology, University of Cambridge; Christine LangleyPostdoctoral Researcher, Cognitive Neurosciences, University of Cambridge; Martine SkumlienPhD Candidate in Psychiatry, University of Cambridgeand Tianye Jiaprofessor of population neuroscience, Fudan University