Ten years after the first legalization of cannabis for recreational use by adults, scientists are seeking to provide science-based guidance on the risks associated with its use among young people.
Dr. Stephanie has been researching how teens use cannabis for two decades, and her observations are worrisome for her teenage son. «I see information coming in, and I know he's going to face it» — she shares.
As a clinical neuropsychologist at the University of Wisconsin-Milwaukee, she helps many young people who have varying experiences with the drug, from a single incident at a party to daily use of potent drugs.
With the increasing legalization of cannabis, the data on its use among young people has become increasingly alarming. According to some studies, nearly a third of teens who regularly use cannabis show signs of a substance use disorder, suggesting that they are unable to stop using it despite negative consequences in their lives.
Dr. Stephanie has been researching how teens use cannabis for two decades, and her observations are worrisome for her teenage son. «I see information coming in, and I know he's going to face it» — she shares.
As a clinical neuropsychologist at the University of Wisconsin-Milwaukee, she helps many young people who have varying experiences with the drug, from a single incident at a party to daily use of potent drugs.
With the increasing legalization of cannabis, the data on its use among young people has become increasingly alarming. According to some studies, nearly a third of teens who regularly use cannabis show signs of a substance use disorder, suggesting that they are unable to stop using it despite negative consequences in their lives.
However, Dr. Stephanie wants more conclusive evidence to discuss the risks associated with cannabis, including issues for her son.
However, it is difficult to decide exactly what to say. Anti-drug campaigns are losing ground, and young people are faced with conflicting messages about risks, in a culture that increasingly portrays cannabis and other previously illicit drugs as safe or potentially beneficial.
«Teens are smart enough to see that adults are using cannabis. This makes general warnings and prohibition virtually useless» — notes Dr. Stephanie.
It's been a decade since cannabis was legalized for recreational use by adults in Uruguay (for those over 18) and in Colorado and Washington State (for those over 21).
However, it is difficult to decide exactly what to say. Anti-drug campaigns are losing ground, and young people are faced with conflicting messages about risks, in a culture that increasingly portrays cannabis and other previously illicit drugs as safe or potentially beneficial.
«Teens are smart enough to see that adults are using cannabis. This makes general warnings and prohibition virtually useless» — notes Dr. Stephanie.
It's been a decade since cannabis was legalized for recreational use by adults in Uruguay (for those over 18) and in Colorado and Washington State (for those over 21).
Many other countries and states have followed suit, and researchers are trying to understand the consequences of this legalization: how drug use patterns are changing, how cannabis affects brain development, and how its use is linked to mental disorders such as depression, anxiety and schizophrenia.
So far, the data are inconclusive: young people do not appear to have started using cannabis more frequently than before legalization, but there are trends towards more problematic use. Frequent use is associated with increased mental health problems and risk of addiction, although there may be other explanations for these observations. Experimental studies on humans and animals could clarify the situation, but they are hampered by the fact that cannabis is still illegal in many places, making it difficult to study its effects.
Hence the concern among some researchers that society could be facing a serious public health problem without proper awareness.
So far, the data are inconclusive: young people do not appear to have started using cannabis more frequently than before legalization, but there are trends towards more problematic use. Frequent use is associated with increased mental health problems and risk of addiction, although there may be other explanations for these observations. Experimental studies on humans and animals could clarify the situation, but they are hampered by the fact that cannabis is still illegal in many places, making it difficult to study its effects.
Hence the concern among some researchers that society could be facing a serious public health problem without proper awareness.
«I worry that it could turn out to be as bad for us as tobacco. Even if the risks of cannabis use are small, it's like playing roulette» — states Nora Volkow, director of the National Institute on Drug Abuse in Bethesda, Maryland.
With the hope of better understanding the situation, her agency is funding the Adolescent Brain Cognitive Development (ABCD) study, which started in 2015 and involves more than 10,000 children between the ages of 9 and 10. The goal is to take annual scans of their brains and track the impact of various factors on their development.
The current project participants are between 16 and 18 years old, and some of them have already been exposed to the drug, said Dr. Stephanie, one of the project leaders. «So we should be able to really assess the impact of early cannabis use» — she commented.
Changing patterns of use
Medical marijuana has been legalized in a number of American states since 1996, but Colorado and Washington became the first to legalize its recreational use through a popular vote in 2012. In 2013, Uruguay became the first country to allow the sale of cannabis for recreational purposes.
There were fears that legalization would lead to an increase in the number of teenagers using the drug, but according to neuroscientist Angela Bryan of the University of Colorado at Boulder, this has not been the case. She states, «Paradoxically, the legalization of cannabis has decreased its use among teens» — at least in her state.
Two years of surveys conducted by the Colorado Department of Public Health and Environment found that cannabis use among students ages 14-18 has declined from about 21 percent in 2005-2019 to 13 percent in 2021. Overall trends across the country appear similar, with one study attributing the decline in use to the COVID-19 pandemic.
However, legalization may have different effects in different regions, notes clinical psychologist James McKillop of McMaster University in Hamilton, Canada. When cannabis was legalized in Canada for adults over 18 five years ago, there was no spike among adolescents. However, consumption increased when illegal stores without a government license began operating, he says.
Two years of surveys conducted by the Colorado Department of Public Health and Environment found that cannabis use among students ages 14-18 has declined from about 21 percent in 2005-2019 to 13 percent in 2021. Overall trends across the country appear similar, with one study attributing the decline in use to the COVID-19 pandemic.
However, legalization may have different effects in different regions, notes clinical psychologist James McKillop of McMaster University in Hamilton, Canada. When cannabis was legalized in Canada for adults over 18 five years ago, there was no spike among adolescents. However, consumption increased when illegal stores without a government license began operating, he says.
«The number of cannabis stores outnumbers Tim Hortons» — McKillop jokes, referring to the famous Canadian coffee shop. There are also definite negative consequences. A recent study in Ontario found that residents living near a cannabis dispensary were more likely to go to hospital with psychosis, which is increasingly being linked to products containing high levels of cannabis' active ingredients.
In Uruguay, after legalization in 2014, there was a temporary increase in use among young people aged 18-21, but according to the survey, this use quickly returned to pre-legalization levels. More to the point, the survey found no increase in the number of teens with addictions or problematic cannabis use.
Ariadna Rivera-Aguirre, a social epidemiologist at New York University who led the study, points to a number of contributing factors. Among them, Uruguay has restrictions on the strength of legally sold products, prohibits advertising, and only allows the sale of cannabis flowers, with no edible or concentrated forms.
In Uruguay, after legalization in 2014, there was a temporary increase in use among young people aged 18-21, but according to the survey, this use quickly returned to pre-legalization levels. More to the point, the survey found no increase in the number of teens with addictions or problematic cannabis use.
Ariadna Rivera-Aguirre, a social epidemiologist at New York University who led the study, points to a number of contributing factors. Among them, Uruguay has restrictions on the strength of legally sold products, prohibits advertising, and only allows the sale of cannabis flowers, with no edible or concentrated forms.
Rivera-Aguirre measured not only the number of adolescents using cannabis, but also the level of problematic use, which many previous surveys did not take into account. The increase in use could be the result of increased media discussion of legalization, she notes. There is a general interest in understanding when casual use becomes a problem.
«I think the focus of research should not be on the typical 17-year-old who smokes a joint at a party» — says Bryan.
While overall use among people under 21 has not increased dramatically, there are concerns about what products are being offered. High levels of delta-9-tetrahydrocannabinol (THC) in products available in stores outside of Uruguay are gaining attention.
«Today's cannabis is much different than it was years ago» — states clinical psychiatrist Ryan Sultan of Columbia University in New York City.
THC concentrations in U.S. Drug Enforcement Administration-approved products have more than tripled since 1996, and many dispensaries offer vaping liquids and products for «dabbing», a method of consuming concentrated THC that can inject significant amounts of the drug into the lungs.
«I think the focus of research should not be on the typical 17-year-old who smokes a joint at a party» — says Bryan.
While overall use among people under 21 has not increased dramatically, there are concerns about what products are being offered. High levels of delta-9-tetrahydrocannabinol (THC) in products available in stores outside of Uruguay are gaining attention.
«Today's cannabis is much different than it was years ago» — states clinical psychiatrist Ryan Sultan of Columbia University in New York City.
THC concentrations in U.S. Drug Enforcement Administration-approved products have more than tripled since 1996, and many dispensaries offer vaping liquids and products for «dabbing», a method of consuming concentrated THC that can inject significant amounts of the drug into the lungs.
Impact of cannabis on adolescent health
Highly effective drugs can significantly increase the risk of psychosis, and some researchers have raised concerns about possible long-term effects. «The psychiatric community is seriously concerned about the link between cannabis and schizophrenia» — says Dr. Emily.
A study of more than 40,000 people diagnosed with schizophrenia in Denmark, where cannabis has been legalized since 2018, found that about 15% of cases can be linked to cannabis use disorder, and the rate is even higher among young men.
However, Carsten Hjorthøj, an epidemiologist at the University of Copenhagen who led the study, emphasizes the unclear causal link between cannabis use and schizophrenia. A possible scenario is that people with schizophrenia use cannabis in an attempt to self-medicate. Similar difficulties arise when examining the relationship between cannabis, depression and anxiety, but clear links do exist.
In another study of nearly 70,000 adolescents in the U.S., Sultan found that about 1 in 40 young people were addicted to cannabis, with an additional 1 in 10 using it without being addicted. Even among this group, young people were twice as likely to suffer from depression and experience other negative consequences such as absences, lower academic achievement and arrests.
Highly effective drugs can significantly increase the risk of psychosis, and some researchers have raised concerns about possible long-term effects. «The psychiatric community is seriously concerned about the link between cannabis and schizophrenia» — says Dr. Emily.
A study of more than 40,000 people diagnosed with schizophrenia in Denmark, where cannabis has been legalized since 2018, found that about 15% of cases can be linked to cannabis use disorder, and the rate is even higher among young men.
However, Carsten Hjorthøj, an epidemiologist at the University of Copenhagen who led the study, emphasizes the unclear causal link between cannabis use and schizophrenia. A possible scenario is that people with schizophrenia use cannabis in an attempt to self-medicate. Similar difficulties arise when examining the relationship between cannabis, depression and anxiety, but clear links do exist.
In another study of nearly 70,000 adolescents in the U.S., Sultan found that about 1 in 40 young people were addicted to cannabis, with an additional 1 in 10 using it without being addicted. Even among this group, young people were twice as likely to suffer from depression and experience other negative consequences such as absences, lower academic achievement and arrests.
Some researchers are working to identify possible mechanisms for the effects of cannabis on mental health, while others are using surveys and medical data to look for correlations. Many hope to get more conclusive results through long-term studies such as ABCD.
Studies that focus on connections at a specific point in time have their limitations. «One has to wonder what is behind the fact that adolescents who use cannabis show higher levels of depression? It could be because cannabis causes depression, or it could be that depressed teens start using cannabis. Or is there some third variable?» — asks Madeleine Meyer, a clinical psychologist at Arizona State University in Tempe.
How does cannabis work on the brain? It mimics endogenous cannabinoid neurotransmitters by activating multiple receptors in the brain. It duplicates this system, but does so with a stronger effect — that is, the highly active THC products significantly activate receptors, compared to normal activity.
Studies that focus on connections at a specific point in time have their limitations. «One has to wonder what is behind the fact that adolescents who use cannabis show higher levels of depression? It could be because cannabis causes depression, or it could be that depressed teens start using cannabis. Or is there some third variable?» — asks Madeleine Meyer, a clinical psychologist at Arizona State University in Tempe.
How does cannabis work on the brain? It mimics endogenous cannabinoid neurotransmitters by activating multiple receptors in the brain. It duplicates this system, but does so with a stronger effect — that is, the highly active THC products significantly activate receptors, compared to normal activity.
In adolescents, one of the main concerns is the ability of THC to easily bind to the CB1 receptor, which is largely responsible for the reward system and executive functions such as memory and decision-making. CB1 receptors are more prevalent in adolescents than in adults.
The researchers aim to find out how long-term use of cannabis, especially with high THC concentrations, can affect mental health and cognitive function.
Meyer and her team analyzed the effects of cannabis use on a group of about 1,000 people born between 1972 and 1973 and found that those who used cannabis frequently showed lower IQ scores than those who smoked less frequently or not at all, with the effect being particularly pronounced in those who started using in their teens.
According to Meyer, her study indicates that infrequent cannabis use during adolescence does not lead to significant cognitive decline. However, as she states, «it is a cautionary tale regarding use». She is most concerned about the risk of further use in those who started at a young age.
The researchers aim to find out how long-term use of cannabis, especially with high THC concentrations, can affect mental health and cognitive function.
Meyer and her team analyzed the effects of cannabis use on a group of about 1,000 people born between 1972 and 1973 and found that those who used cannabis frequently showed lower IQ scores than those who smoked less frequently or not at all, with the effect being particularly pronounced in those who started using in their teens.
According to Meyer, her study indicates that infrequent cannabis use during adolescence does not lead to significant cognitive decline. However, as she states, «it is a cautionary tale regarding use». She is most concerned about the risk of further use in those who started at a young age.
Meyer also points out a flaw in her study, as it does not take into account other factors that affect cognitive function, such as genetics and socioeconomic status.
Joseph Henrich emphasizes that all criticisms were taken into account in the design of the ABCD study. It involves 10,000 children from different social backgrounds and aims to obtain a diverse group of active cannabis users. During this study, researchers will examine participants' brains, track their test scores and assess cognitive function, while the participants themselves answer questions about their contact with drugs. Many believe that this study will help create the most comprehensive understanding of the effects of cannabis.
The importance of research on the possible long-term effects of high THC concentrations is also of interest to scientists, as many participants may eventually begin to try such products. In the U.S., efforts to study cannabis are complicated by the fact that it remains illegal at the federal level. Research institutions only have access to one type of cannabis, known for its low potency compared to those products sold in stores or on the black market.
Joseph Henrich emphasizes that all criticisms were taken into account in the design of the ABCD study. It involves 10,000 children from different social backgrounds and aims to obtain a diverse group of active cannabis users. During this study, researchers will examine participants' brains, track their test scores and assess cognitive function, while the participants themselves answer questions about their contact with drugs. Many believe that this study will help create the most comprehensive understanding of the effects of cannabis.
The importance of research on the possible long-term effects of high THC concentrations is also of interest to scientists, as many participants may eventually begin to try such products. In the U.S., efforts to study cannabis are complicated by the fact that it remains illegal at the federal level. Research institutions only have access to one type of cannabis, known for its low potency compared to those products sold in stores or on the black market.
«Some types of research are simply not done because of their complexity. There are additional costs involved and the need for more specialists» — says R. Lorraine Collins, a psychologist at the University of Buffalo. Also, the cost of research cannabis is frustrating for participants, as psychiatrist Jesse Hinckley notes.
Some researchers have found alternative ways to study cannabis on the street. Brian and his team in Colorado have converted several vans into mobile labs, which they call canna-vans, to test users' blood before and after using the drug. The researchers have begun expanding their work to teenagers.
Volkov is trying to adapt cannabis research to the current state of affairs — a focus on vaping, dabbing and edibles. Meanwhile, Dr. Stephanie is preparing for the next phase of the ABCD study. At this point, most of the participants are 16-18 years old — the age when they are expected to start using cannabis. When talking to youth and their parents, she notices a lack of clear guidance on how to safely handle cannabis, forcing her to provide advice on a case-by-case basis.
Some researchers have found alternative ways to study cannabis on the street. Brian and his team in Colorado have converted several vans into mobile labs, which they call canna-vans, to test users' blood before and after using the drug. The researchers have begun expanding their work to teenagers.
Volkov is trying to adapt cannabis research to the current state of affairs — a focus on vaping, dabbing and edibles. Meanwhile, Dr. Stephanie is preparing for the next phase of the ABCD study. At this point, most of the participants are 16-18 years old — the age when they are expected to start using cannabis. When talking to youth and their parents, she notices a lack of clear guidance on how to safely handle cannabis, forcing her to provide advice on a case-by-case basis.
«I strive to provide teens and adults with information so they can make more informed decisions» — says Dr. Stephanie.
She also hopes to find out what amount of cannabis is considered too much and what factors increase the risk of developing a use disorder. These parameters can vary from person to person and can include genetic traits and even brain structure.
This information can be helpful in conversations with her own son, who has high academic goals. «I have noticed that cannabis negatively affects aspects such as thinking speed, complex attention and short-term memory, which affects his grades». At this point, she hopes the warnings about the risks will be meaningful to him.
She also hopes to find out what amount of cannabis is considered too much and what factors increase the risk of developing a use disorder. These parameters can vary from person to person and can include genetic traits and even brain structure.
This information can be helpful in conversations with her own son, who has high academic goals. «I have noticed that cannabis negatively affects aspects such as thinking speed, complex attention and short-term memory, which affects his grades». At this point, she hopes the warnings about the risks will be meaningful to him.