How can prolonged recreational cannabis use affect our mental health? While there is still a lot of research to be done, the WHO has recently published a review of the available studies.
In the past twenty years, the landscape of recreational marijuana use changed dramatically. The total number of U.S. states to legalize marijuana approached 24. The majority of those states allowed cannabis for medical use, however, recreational pot is fully legal in Colorado, Washington, Alaska, Oregon, and the District of Columbia.
The World Health Organization (WHO) decided to summarize the available knowledge on cannabis by publishing a report on the health consequences of non-medical cannabis use, with a special focus on the long-term use and the effects of marijuana on youngsters. This milestone report, titled “The health and social effects of non-medical cannabis use,” is based on the best available studies on the subject by a broad range of researchers, scientists, and experts from all corners of the world.
The main goal of the WHO was to publish the latest information on the effects of recreational cannabis use on physical and mental health. In this report, you could find everything you should know about the relationship between long-term marijuana use and mental health problems.
Among the potential long-term mental effects of cannabis, there are cognitive impairment, mental disorders (including depression, psychoses, schizophrenia, and others), suicidal tendencies, and dependence.
In 1994, a group of scientists published a study that examined whether cannabis use can impair cognitive performance. They found that the regular marijuana users had poorer cognitive performance than non-using controls.
Since then, it has been proved that cannabis use may cause significant “deficits in verbal learning, memory and attention in regular cannabis users.” The degree of the effect depends on the duration and the frequency of use, the potency and dose of the consumed product, and individual factors.
Most researchers agree with the statement that there is an association between long-term cannabis use in adolescence and verbal memory impairment. That means that marijuana may really affect on IQ and memory of heavy users. However, the poorer cognitive performance may result from socioeconomic circumstances of people who use cannabis, rather than from cannabis use itself. For example, teenagers who use marijuana are much more likely to also use alcohol, cigarettes, and other illicit drugs that predict lower IQ scores and school performance. They also are likely to have social adversity during adolescence.
“MRI studies have reported structural changes in the hippocampus, prefrontal cortex and cerebellum in chronic cannabis users” and the longer the user consumes marijuana, the bigger changes have been observed. According to a 2008 study of brain structure and function in chronic marijuana users, there is a consistent reduction in hippocampal volume.
Although there are some findings that marijuana may cause IQ decline, it is unlikely that cannabis use is the only reason of poor cognitive performance. Those who start using marijuana at a young age often have more behavioral difficulties and less stable background than non-smokers. Moreover, youngsters with poorer IQ are more likely to become regular marijuana users, so we face a classic “chicken or egg” causality dilemma.
When it comes to cannabis dependence, the WHO defines this a complex of behavioral, cognitive, and psychological phenomena that develop after prolonged repeated use of marijuana. Cannabis dependence is currently the most common form of the drug-use disorder among adults and teenagers in the United States, Canada, and Australia. Some studies estimate the risk of dependence for those who begin using cannabis in adolescence as 16 percent. Conditional on the specific diagnostic criteria for dependence, the risk may go up to 50 percent for heavy marijuana users.
Before discussing the relationship between cannabis use and mental disorders, let us figure out what psychosis, depression, and schizophrenia are.
This is how the WHO defines the term “schizophrenia”: A mental and behavioral disorder characterized by distortions in perception, thinking, behavior, language, emotions, and sense of self. People suffering from this disorder often hear voices and experience delusions.
Psychosis is not a mental health disorder, but a general term used to describe psychotic symptoms, including schizophrenia and depression.
The researchers found the link between the dose and frequency of cannabis use at the young age and the risk of schizophrenia. People under 18 who had tried the drug were 2,4 times more likely to experience the psychiatric disorder over the next fifteen years compared to those who had never tried cannabis.
The researchers estimated that 13 percent of cases of schizophrenia would have been averted if none of study participants used cannabis. This seems to support the hypothesis that individual factors (childhood abuse, genetic risk) may increase the risk that teenagers will use cannabis and develop schizophrenia. Certain studies suggest that shared genetic factors may explain some, though not all, of the association between marijuana and psychosis.
Psychotic syndromes have been reported in people used cannabinoid extract Sativex as the part of their treatment. For example, a recent study suggests that long-term use of weed with high levels of THC and low levels of CBD increases the risk of developing schizophrenia in teenagers by up to five times.
Although the relationship between the regular cannabis use and depression are much weaker than between marijuana and psychosis, scientists claim that people suffering from cannabis-use disorders “have higher rates of anxiety, conduct disorders, eating disorder and personality disorders.” Many of these studies, however, failed to account for the possibility that depressed people are more likely to use cannabis.
Overall, studies on marijuana use and suicide cases produced mixed, sometimes diametrically opposite, results. One study of serious suicide attempts in New Zealand found a positive correlation between cannabis use and the number of suicide cases while a small study in the USA was not able to find any.
The researchers insist that the lack of homogeneity in the measurement of cannabis exposure across studies and the lack of systematic control are significant obstacles to the development of this field of studies.