4 Marijuana and Brain Development in Adolescents

Introduction

Opinions on marijuana have varied through the years. It went from a drug feared to cause violent acts and lead to insanity in the 1930s to being seen as a potential medication for cancer pain and seizures in the 2010s. As a result, a few states have legalized the medicinal and recreational use of marijuana. However, recreational marijuana may be harmful when misused, especially in adolescence (ages 10 to 19). As of 2018, six percent of 12th graders, three percent of 10th graders, and one percent of 8th graders reported daily cannabis use in the United States (Hammond et al., 2020). Cannabis produced today contains higher levels of THC (see Chapter 5 for more information). With the introduction of edibles as a source of marijuana, it is easier to ingest excessive amounts of THC without realizing it (Centers for Disease Control, 2021; Testai et al., 2022).

What is Marijuana?

Cannabis refers to products from the Cannabis sativa plant (National Center for Complementary and Integrative Health, 2019). Marijuana refers to the dried leaves, flowers, stems, and seeds from the Cannabis Sativa plant that contains tetrahydrocannabinol (THC) and cannabidiol (CBD) (National Institute on Drug Abuse, 2019). Marijuana has both medicinal use and recreational use. Medicinal marijuana is cannabis taken orally or by nasal spray to relieve symptoms of a medical condition (Alcohol and Drug Foundation, 2022). Medical marijuana may help with seizures, pain, anxiety management, and help with reducing inflammation. Recreational marijuana is cannabis used for personal enjoyment (Leafly, n.d.). Unlike medical marijuana, recreational marijuana contains more THC, the chemical responsible for feeling high.

History of Cannabis

When first introduced to America in the 1600s, cannabis was primarily grown to make clothes, ropes, sails, paper, and oil (History.com, 2017). The unique medicinal and recreational properties helped increase the spread of cannabis worldwide. It was not until the late 19th century that marijuana became used in medicine (University of Georgia, n.d.). However, increased immigration from Mexico negatively impacted attitudes around cannabis (University of Georgia, n.d.). Marijuana had become a drug that those of a higher socioeconomic status feared for its addicting and violence-causing capabilities, both of which are myths (Siff, 2014). By 1931, 29 states had passed laws prohibiting marijuana. By 1937, the Marijuana Tax Act was passed (University of Georgia, n.d.).

In 1970, Congress classified marijuana as a Schedule 1 drug by the Comprehensive Drug Abuse Prevention and Control Act (Siff, 2014). As a Schedule 1 drug, Congress deemed marijuana to have no accepted medical use and a high potential for abuse (United States Drug Enforcement Administration, n.d.). However, a few states began legalizing the use of marijuana, with California being the first state to legalize medical marijuana in 1996. Currently, 21 states have legalized the medical and recreational use of marijuana (M.J. Biz Daily, n.d.). Other states have enacted decriminalization laws (NORML, n.d.).

Effect of Legalization

Since the legalization of cannabis, few adolescents have perceived it as harmful. It has become more socially acceptable and seen as beneficial to health (Mennis et al., 2023; Geoffrion, n.d.). In 2018, about 1.6 million adolescents aged 12 to 17 used cannabis (Hammond et al., 2020). In 2022, roughly 30.7% of high school seniors reported using cannabis (National Institute on Drug Abuse, 2020b). Many adolescents are exposed to ads promoting edibles, vapes, and other cannabis products. In 2019, roughly one in three youth in states with legal recreational use interacted with marijuana brands on social media (University of Wisconsin-Madison, 2019). According to the University of Wisconsin-Madison, engaging with marijuana marketing is linked to adolescents’ being five to eight times more likely to use marijuana.

Effects of Marijuana on Adolescents

Effect on Brain Structure

The brain continuously develops from the moment of birth up until age 25. In adolescence, certain areas of the brain that affect impulse control, social behavior, and planning start to develop. During this time, the brain also undergoes maintenance, removing unused connections and improving those used to increase cognitive functioning (Dhein, 2020). Marijuana interacts with specific receptors within the brain, increasing or decreasing dopamine and glutamate levels in the brain. These receptors are involved in various activities, from appetite and memory to pain and inflammation (Genetic Science Learning Center, n.d.; Zou & Kumar, 2018; Testai et al., 2022; Ye, Cao, Wan, & Zhou, 2019).

However, some research has shown that heavy cannabis use can damage adolescent development (Dhein,2020; De Felice et al., 2023). Early cannabis use may thin or reduce the number of neurons that develop in specific brain areas, impairing the connection between locations (Dhein, 2020; Schmidt, 2021; Blest-Hopley et al., 2020). Areas of the brain affected by marijuana use include the hippocampus and the prefrontal cortex.

Effect on Brain Function

These structural changes and disruptions in normal brain development in youth could contribute to more significant and long-lasting changes in behavior and memory (Schmidt, 2021). Heavy cannabis use during adolescence may impair planning, abstract thinking, and impulse control (Weir, 2015). Other effects associated with marijuana use include poor memory, lack of motivation, trouble managing emotions, and poor sleep quality (Volkow et al., 2016; Jacobus et al., 2010). Additionally, daily use of marijuana during adolescence can increase the risk of addiction and the development of a cannabis use disorder (Geoffrion, n.d.). In 2017, 2% of adolescents aged 12 to 17 met the definition of cannabis use disorder (Hammond et al., 2020). Chapter 5, “Marijuana Overconsumption and Tolerance” discusses cannabis use disorder further. Overall, marijuana use can lead to difficulties in learning and lower intelligence (National Institute on Drug Abuse, 2021).

Social Impact of Marijuana Use

The effects of cannabis on the brain can negatively impact their future social standing and well-being. As a result of the impairments in learning, adolescents who used marijuana tended to have lower academic outcomes, leading to poor economic outcomes by their early 30s (Eckart, 2019). Poor educational development impacts racial and ethnic minorities more within the United States than those who are not. Racial and ethnic minorities may lack access to resources promoting academic achievement (Cyrus et al., 2021). Marijuana is also associated with a risk of developing or worsening mental health disorders such as anxiety and depression (Ali et al., 2019). Cannabis use may also increase risky behaviors and lead to a dependency on cannabis, negatively impacting future relationships (Ali et al., 2019; Ekcart, 2019).

Conclusion 

Daily use of cannabis may reduce the number of neurons in some brain regions, impacting the brain’s ability to connect and send messages to each area. Cannabis can impair adolescents’ learning capabilities and increase the risk of developing a cannabis use disorder. Multiple interventions out there address cannabis use and substance use in general in the adolescent population, including Teen Marijuana Check-Up, which showed greater decreases in cannabis use compared to adolescents who did not use it. It has even been shown that a brief, three-session intervention based on motivational interviewing and cognitive behavior therapy can help to reduce cannabis use in adolescence (Winters et al., 2021).

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