Since the last decade, the global use of marijuana has risen by 60%. In 2019, 200 million people used marijuana, and the number continues to rise. Even so, we still know very little about the consequences of marijuana on human cognition, whether because of conflicting research results or little concrete evidence of its long-term effects.
This year, Sorkhou, Bedder, and George (2021) published a systematic review that analyzes 124 studies conducted between 1995 and 2020 on how recreational marijuana use affects mental health. They identify four main areas that are negatively affected by marijuana.
1. Cognition
The chronic use of marijuana impacts certain cognitive functions, such as memory, decision making, and attention. Excessive use leads to greater memory lapses, especially among participants who started using marijuana as teenagers.
They also found that cognitive problems that occur while users are high were greater among participants who did not create tolerance to marijuana, which means that those who are more frequent and heavy users do not feel the effects on cognition as much.
2. Motivation
Because it is a difficult concept to analyze in a standardized way, there is not much evidence about the effect of marijuana on motivation. However, the results found show that chronic use can lead to reduced motivation, loss of desire to work or compete, and decreased interest in creating and meeting goals.
3. Psychosocial functioning
A considerably high amount of data shows that developing young people who use marijuana are less likely to finish high school or complete a college degree. High school students who are regular users are less likely to go to class, complete homework, and achieve and value good grades.
There is evidence to suggest that people who start using in adolescence and who make frequent use of marijuana are less economically successful compared to the general population.
A study in New Zealand followed a group of children up to middle age while tracking their marijuana use. Participants were more prone to chronic use when diagnosed with conduct disorder, had parents who also used it, or suffered trauma during childhood. Participants who used it frequently as adults were more likely to suffer from mental health problems and abuse other substances.
4. Risk of psychiatric disorders
There is evidence that the frequent use of marijuana leads to mental health problems, but this matter is complex, and its mechanism cannot be explained with the data we have. Many studies show that for those who started using in adolescence, the higher the marijuana use, the more likely they are to experience depressive symptoms. However, studies are inconsistent, and some do not address other important factors, such as tobacco and alcohol use.
Studies on marijuana and anxiety are also inconsistent. Some show that the use of marijuana leads to anxiety symptoms. But other studies with cannabidiol, or CBD, show that CBD helps in reducing anxiety.
However, the evidence is clear about psychosis: there is a strong association between frequent use of marijuana in adolescence and psychosis, a condition in which the mind loses contact with reality.
In conclusion, the data show that the use of marijuana, especially when frequent and/or during youth when the brain is still developing, leads to mental health problems that can affect the consumer's education and occupation options.