Cannabis use is extremely common among adolescents and young adults, with an estimated 14% of students in the 10th grade, 23% of students in the 12th grade, and 22% of college students and young adults engaging in at least monthly use in 2016.1 In 2015, 1.8 million adolescents (aged 12-17 years) and 6.9 million young adults (aged 18-25 years) were current users of cannabis.2 Moreover, the problem is increasing: 30-day prevalence of use among students in the 12th grade rose from 19% in 2007 to 23% in 2017.3 There is even higher use in Canada: In 2013, an estimated 28% of youths aged 11 to 15 years admitted to using cannabis at least once a year, and a high number reported weekly or daily use.4
The National Institute on Drug Abuse reports that cannabis use is more prevalent among males than females, indicating a sex gap that is continuing to widen.5 The effects of the drug also differ between the sexes, in that males show a greater cannabis-induced high compared with their female counterparts.6 By 9th grade, approximately 1 in 3 boys and 1 in 4 girls will have used cannabis.7 A survey of more than 2000 cannabis users found that men reported using cannabis more frequently and in higher quantities than women, and were also more likely to use joints/blunts, vaporizers, and concentrates, whereas women were more likely to use pipes and oral administration.8
“We are in the midst of a huge epidemic of young people using marijuana,” observed Meldon Kahan, MD, Associate Professor, Department of Family Medicine, University of Toronto, and Medical Director of the Substance Use Service at Women’s College Hospital, Toronto, Ontario, Canada.
“The epidemic is driven partially by changed attitudes toward its use and by legalization, but is driven largely, at least in Canada, by cannabis companies that are pushing it to this age group and claiming it’s safe, while in reality, it’s anything but safe,” he told Psychiatry Advisor.
Cannabis consists of numerous compounds, but the central 2 are cannabidiol (CBD) and Δ-tetrahydrocannabinol (THC), which is responsible for the psychoactive effects that occur via its interaction with the endocannabinoid system.9 Adolescents typically do not think that cannabis use is as risky as other substances, a belief that has been “steadily growing.”1 When asked, “How much do you think people risk harming themselves if they smoke marijuana regularly?” less than one-third of high school seniors responded that there was a “great risk” in 2016 compared with 58% in 2006.1 The pervasiveness of cannabis, together with its “relatively low lethality,” has led to the misperception among adolescents and adults alike that it is innocuous9; for example, many baby boomers who used cannabis when they were in college have resumed use.10 However, the amount of THC is considerably higher than it was in the 1960s and 1970s, with rates that continue to climb. THC levels in cannabis have risen from 8.9% in 2008 to 17.1% in 2017, and the mean THC:CBT ratio also rose substantially, going from 23 in 2008 to 104 in 2017.11
Cannabis use in adolescence is associated with harmful outcomes during adulthood (eg, adverse social behaviors,12 decreased neuropsychological and cognitive function,13 and increased risk for depression, anxiety, and suicidality14).
Moreover, during adolescence, cannabis is associated with increased psychiatric emergency department (ED) visits15,16 and increased risk for psychosis,17 with some research suggesting that it might as much as double the risk for psychosis and schizophrenia.18
Misperceived Benefits: Adolescent ADHD and Anxiety
In addition to sometimes inaccurate safety perceptions, there is an “increasingly popular perception” that cannabis is beneficial for attention-deficit/hyperactivity disorder (ADHD), and many individuals with the condition are turning to cannabis for relief of symptoms such as poor concentration or hyperactivity.19
“In the past month, I have treated 6 young men — adolescents or young adults — who presented to the ED with psychosis induced by vaping high-potency cannabis,” Wilfrid Noel Raby, PhD, MD, Adjunct Assistant Clinical Professor, Albert Einstein College of Medicine, Bronx, New York, told Psychiatry Advisor.
“It could be that the cannabis temporarily overrides some of the deficits that are associated with ADHD; for example, more aberrant frontal lobe functioning or hyperactivity,” he suggested.
However, “many of these youngsters are also taking stimulants, and stimulants can work synergistically with THC when consumed in low quantities, since THC can also have excitatory effects. In fact, many people get agitated when using it,” Dr Raby pointed out.
In contrast, “I’ve had people tell me that marijuana balances out the stimulant effects and adds relaxation when smoked in higher quantities, but the excessive glutamate release from the combination of THC and stimulants can lead to psychosis.”
The dose and potency of cannabis are very important, Dr Raby noted.
“We know that cannabidiol can have inhibitory effects that protect against the psychoactive and stimulating effects of THC alone, and there may be other cannabinoids contained in cannabis that have a similar effect,” he said.
“But vaping a product that is almost exclusively THC means that there is nothing to counterbalance it,” he explained.
Many youngsters and adults associated cannabis with relaxation or relief of insomnia, Dr Kahan added. “Patients who would like to reduce anxiety, increase sleep, or address pain should look specifically for products made exclusively or primarily with CBD,” he recommended.
Cannabis and the Adolescent Brain: Vulnerability to Psychosis
Whether adolescents are using cannabis recreationally or medicinally, Thorsten Rudroff, PhD, Assistant Professor, Department of Health and Human Physiology and Department of Neurology, University of Iowa, Iowa City, cautions, “Adolescence and young adulthood are critical periods in which the use of a high-THC product can have a big effect on the structure and function of the developing brain.”
“Blood flow and glucose metabolism may be impaired in regions associated with maturation, especially when cannabis is being used together with alcohol, as many young people do,” he told Psychiatry Advisor.
Cannabis has been found to be involved in as much as 50% of cases of psychosis, schizophrenia, and schizophreniform episodes.20 Although the exact neurobiological processes are not fully understood,20 there are several hypothesis explaining the association.
“The endocannabinoid system is critical for neurodevelopment and as such is present in early development, and maintains expression throughout life.”9 Numerous important changes take place in the brain during adolescence; in particular, neuronal maturation and rearrangement processes (eg, myelination, synaptic pruning, and dendritic plasticity).21
“Exogenously ingested cannabis produces supraphysiologic effects at [endocannabinoid]-targeted receptors and thus usurp[s] the normal endocannabinoid system,”9 resulting in a “cascade of neurochemical and neurostructural aberrations.”21 Synaptic plasticity may be impaired in schizophrenia, and it is likely that the effect of cannabis on neuroplasticity of the developing brain may play a role in the vulnerability to psychosis.20
Moreover, the disruptions in brain development caused by neurotoxic effects of regular cannabis use might significantly alter neurodevelopmental trajectories, not only by changing neurochemical communication and genetic expression of neural development but also by having a toxic effect on brain tissue itself.21
In addition, individuals at familial risk for psychosis have an increased sensitivity to the effects of cannabis, suggesting a biological interaction between cannabis use and underlying genetic vulnerability.22
“THC affects regions of the brain that are responsible for psychosis and hallucinations,” Dr Rudroff wrote. He noted that in his research, which focused on the use of cannabis in people with multiple sclerosis, his team looked at the effect of both THC and CBD on glucose uptake in the brain.23
“THC caused increased glucose metabolism in the left temporal area, a region associated with executive dysfunction and psychosis, which is especially problematic in patients with [multiple sclerosis] because they already have brain impairments that can lead to psychosis,” he explained. Although CBD may have some medical benefits, “the medical benefits of THC are unclear and debatable,” Dr Rudroff added.