Studying adolescent cannabis use for two decades, Krista Lisdahl worries about her teenage son."I see the data coming in; I know he'll come across it," she says.
As a clinical neuropsychologist at the University of Wisconsin–Milwaukee, Krista Lisdahl observes diverse encounters with cannabis among young people. Instances range from occasional use at parties to daily consumption of potent forms. With global efforts to legalize recreational cannabis, these interactions have surged. In her studies, approximately one-third of regular adolescent users exhibit signs of a cannabis use disorder—persistent use despite adverse effects. Seeking more conclusive evidence, especially concerning her son, she aims for a comprehensive understanding of the drug's risks for youth.
Navigating messaging challenges is daunting. Anti-drug campaigns decline, leaving youth amidst conflicting views. In a culture normalizing cannabis and other once-taboo substances, teenagers confront mixed signals on potential harm or therapeutic benefits. Krista Lisdahl notes teenagers' perceptiveness as they witness adult cannabis use, rendering conventional warnings ineffective.
A decade post-legalization in Uruguay, Colorado, and Washington, researchers strive to understand evolving usage patterns, cannabis's impact on brain development, and its correlation with mental health conditions. As more states and countries adopt similar measures, the urgency to comprehend these aspects intensifies.
Current data lack clarity; youth usage post-legalization remains inconclusive, but trends suggest problematic use. Frequent consumption correlates with increased mental health issues and addiction risk, though alternative explanations exist. Experimental studies face challenges due to cannabis's illegal status in various locations. Additionally, studying accessible products and potencies proves challenging.
Researchers express concern that society may unknowingly face a significant public-health issue. Nora Volkow, Director of the National Institute on Drug Abuse, compares the potential impact to the tobacco epidemic, emphasizing the unpredictability of cannabis use risks, likening it to playing roulette.
To better understand the situation, Nora Volkow's agency funded the Adolescent Brain Cognitive Development (ABCD) study in 2015. Enrolling over 10,000 children aged 9-10, the study aims to capture annual brain images and track developmental influences. With participants now aged 16-18, some are encountering cannabis. Co-leading the project, Krista Lisdahl anticipates measuring the impact of cannabis initiation through the study's comprehensive data.
Changing patterns of use
Since 1996, medicinal cannabis has been legal in parts of the U.S. Colorado and Washington pioneered recreational legalization in 2012, followed by Uruguay in 2013. Despite concerns, Angela Bryan, a neuroscientist in Colorado, notes a paradox: cannabis legalization has not led to an adolescent usage surge. In fact, she observes a decrease in use among adolescents, at least in her state.
Biennial surveys by the Colorado Department of Public Health and Environment reveal a decline in cannabis use among students aged 14–18, dropping from a stable 21% (2005–19) to 13% in 2021. Nationwide, a similar dip aligns with a study linking it to the COVID-19 pandemic.
James MacKillop, a clinical psychologist at McMaster University, notes that the impact of legalization varies across regions. In Canada, where cannabis was legalized for adults 18 and older five years ago, there wasn't an initial spike in adolescent use. However, a surge occurred with the opening of unlicensed, illegal cannabis stores, highlighting the nuanced effects of legalization.
"There are more cannabis storefronts than there are Tim Hortons," notes James MacKillop, highlighting the proliferation of cannabis dispensaries in Canada. Negative consequences are surfacing, as a study in Ontario reveals that residents near a dispensary were more likely to seek hospital treatment for psychosis. This trend is linked to the rising use of high-potency cannabis products.
Uruguay witnessed an initial usage spike among 18 to 21-year-olds after legalization in 2014, followed by a return to pre-legalization levels, as indicated by survey results. Contrary to fears, there was no increase in adolescent addiction or problematic cannabis use. Ariadne Rivera-Aguirre, a social epidemiologist at New York University, suggests various factors at play, including Uruguay's legal limits on product potency, restrictions on advertising, and the exclusive sale of cannabis flower products, excluding edibles or concentrates.
Ariadne Rivera-Aguirre's study not only assessed the prevalence of adolescent cannabis use but also examined problematic usage levels, often overlooked in past surveys. The initial spike in use could be attributed to heightened discussion and media coverage of legalization, according to Rivera-Aguirre. Many researchers, including Angela Bryan, emphasize the need to shift research focus towards understanding when casual use transitions into problematic patterns, rather than fixating on typical scenarios like a 17-year-old having a joint at a party.
While cannabis use hasn't surged in individuals under 21, concerns arise about the products sold. Outside Uruguay, dispensaries increasingly offer cannabis with significantly higher delta-9-tetrahydrocannabinol (THC) concentrations, warns Ryan Sultan, a clinical psychiatrist at Columbia University. He notes the stark evolution in cannabis potency, emphasizing that today's products differ greatly from those in the past. US Drug Enforcement Administration data indicate a more than threefold increase in THC concentration since 1996. Many dispensaries now provide vaping fluids and 'dabbing' products, a method delivering concentrated THC into the lungs, raising apprehensions about potential health implications.
Health impacts
High-potency cannabis preparations pose elevated risks of inducing psychosis, raising concerns among researchers about potential long-term effects. Ryan Sultan, a clinical psychiatrist at Columbia University, emphasizes the psychiatric community's deep concerns about the connection between cannabis use, particularly high-potency products, and schizophrenia.
In Denmark, where cannabis has been legal since 2018, a study of over 40,000 people with schizophrenia reveals that approximately 15% of cases can be linked to cannabis use disorder. This association is notably higher among young men, underscoring concerns about the potential impact of cannabis use on mental health.
Carsten Hjorthøj, an epidemiologist at the University of Copenhagen, who led the study in Denmark, notes uncertainty about the causal nature of the association between cannabis and schizophrenia. It remains unclear whether cannabis use contributes to schizophrenia or if those with schizophrenia are using cannabis for self-medication. Similar challenges exist in understanding the links between cannabis and depression or anxiety, despite the observable associations.
In a study of nearly 70,000 U.S. adolescents, Ryan Sultan discovered that approximately 1 in 40 were addicted to cannabis, while another 1 in 10 used cannabis without addiction. Even among non-addicted users, young people were twice as likely to face depression episodes and other adverse outcomes, including school absenteeism, lower grades, and increased likelihood of arrest. These findings underscore potential negative consequences associated with cannabis use in adolescence.
Researchers explore potential mechanisms linking cannabis to mental health, using surveys and health records. Long-term studies like ABCD are anticipated to yield more conclusive results. Single-point studies face limitations in establishing causation. Madeline Meier, a clinical psychologist at Arizona State University, questions whether the observed higher depression levels in adolescent cannabis users stem from cannabis-induced depression, self-medication by depressed adolescents, or an unidentified third variable. The complexity underscores the challenges in pinpointing the dynamics between cannabis use and mental health outcomes.
What’s going on in the brain?
Cannabis mimics natural cannabinoids, activating brain receptors, particularly CB1, associated with reward, memory, and decision-making. High-potency THC products, while mimicking the system, overly stimulate receptors, raising concerns. In adolescents, CB1 is more prevalent, posing heightened risks to brain functions like executive functioning. Krista Lisdahl notes that cannabis, especially high-potency THC, essentially "cheats the system" by significantly intensifying receptor stimulation compared to routine activities.
Researchers, including Madeline Meier, investigate the impact of prolonged cannabis use, particularly high-THC products, on mental health and cognitive function. Analyzing a group born between 1972 and 1973, they discovered that consistent cannabis users scored lower on average IQ tests compared to less frequent users or non-users. The most significant effects were observed in individuals who initiated cannabis use during adolescence, highlighting potential long-term cognitive implications associated with early cannabis use.
Madeline Meier's research suggests that infrequent cannabis use in adolescence may not lead to significant cognitive decline, but caution against use is warranted. Concerns lie in the higher risk of long-term use for those who start during adolescence. Critics note the study's limitation in not accounting for factors like genetics and socio-economic status that affect cognitive function.
The Adolescent Brain Cognitive Development (ABCD) study, designed with these concerns in mind, aims to offer a comprehensive view. By recruiting a diverse group of 10,000 children, tracking brain imaging, academic scores, and cognitive function, researchers anticipate a more accurate portrayal of cannabis effects. The study's timing allows insight into long-term effects of high-potency THC products. Challenges in studying such products in the U.S. due to federal cannabis illegality hinder research, pushing some to creative solutions like mobile laboratories.
Researchers like Nora Volkow adapt studies to the evolving cannabis landscape, including vaping and edibles. Krista Lisdahl, preparing for the ABCD study's next phase, emphasizes the need for concrete guidance on cannabis safety. Understanding individual thresholds for cannabis use disorder, considering genetics and brain structure, is crucial. Lisdahl, driven by concerns for her own son, hopes to provide informed guidance to teens and adults facing decisions about cannabis use.
