Introduction

Teenage cannabis usage has grown in popularity recently, and it has serious long-term effects on mental health.¹ In the US, 30.7% of 12th graders reported using cannabis within the previous year in 2022, and 6.3% reported using it daily within the previous month.² Nearly 6% of 15 to 16-year-olds worldwide reported using cannabis in the previous year, indicating that this trend is not just present in the United States. According to one study, nearly one in five teens had used cannabis regularly between the ages of 13 and 17, with greater rates among males (26.6%) than females (9.8%). This indicates that cannabis usage among teenagers is alarmingly common.³ According to another source, over 2.5 million teenagers in the United States, or almost 10% of the population, used cannabis occasionally.⁴

It is essential to be aware of the long-term effects of cannabis usage on adolescent mental health. This is because the juvenile brain is not fully developed until the age of 25 years old approximately.⁵ Cannabis usage during this crucial time may have long-lasting consequences on the developing brain, according to research, especially if it is used frequently or heavily. The purpose of this article is to examine the long-term impacts of cannabis on teenage mental health, with a particular emphasis on the connection between cannabis usage among adolescents and the emergence of mental illnesses such as suicidality and depression, the effects of cannabis usage on young people's cognitive abilities and academic achievement, the possible connection between early cannabis usage and adult substance use disorders, and the long-term cannabis use beginning in adolescence, and how it affects society. 

Understanding cannabis and its psychoactive components

Cannabis contains more than 100 different cannabinoids, it has attracted a lot of attention because of its possible effects on mental health, especially in teenagers. Cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) are the two main substances of interest, they have different and occasionally conflicting effects on the body and brain.⁶ The "high" associated with marijuana use is caused by THC, the primary psychoactive component of cannabis. It functions as a partial agonist by attaching itself to the brain's CB1 receptors and influencing the release of several neurotransmitters, such as acetylcholine,¹ glutamate, and dopamine.⁶ Changes in mood, memory, and cognitive performance can result from this. On the other hand, CBD does not have any psychotropic effects and may even have the opposite effect of THC.^6,7 Since it has been shown that CBD may have anti-psychotic and anti-anxiety effects, interest in its potential medicinal uses has grown.⁷

The effects of cannabis, specifically the THC, are most harmful to the adolescent brain, which doesn’t fully develop until the age of around age 25.⁶ Frequent or excessive usage during this crucial time may affect brain development and function long-term. THC has the ability to alter brain activity, specifically in regions which are essential for memory and learning.⁶ Early cannabis usage has been linked in studies to a higher chance of psychiatric conditions such as anxiety, sadness, and even psychotic disorders later in life.^8,9 Cannabis usage during adolescence may also affect cognitive abilities like executive function, memory, and attention, which could have an impact on future employment opportunities and academic achievement.⁸

Recreational versus medical use

Making the distinction between cannabis usage for medical and recreational purposes is crucial when examining the drug's long-term consequences on teenage mental health. Higher THC concentrations are often used recreationally, with the main goal being to get "high”.

The biggest threat to teenage brain development and mental health is this kind of usage, particularly when excessive or frequent.¹⁰ Conversely, medical use may prioritise CBD-rich strains or products and frequently entails more regulated dosing. CBD is being considered for therapeutic uses because of the possible anti-psychotic and anti-anxiety effects.⁷ Given the continued brain development during adolescence, even medically approved use should be approached with care. It is crucial to warn teenagers, parents, and medical professionals about these possible long-term effects so they can make wise decisions about cannabis use as legalisation and social acceptance of the drug increase.

Adolescent brain: A critical window of development

The brain goes through a second burst of neuronal growth during adolescence, similar to what happens during infancy. A "rewiring" process ensues after this growth and lasts until the age of around 25.¹¹ Two important processes take place during this period:

• Synaptic pruning: Removing unnecessary synapses, it improves neuronal connections. Impulse conduction throughout the neurocircuitry is accelerated by myelination¹¹
• Prefrontal cortex: It governs decision-making, self-control, and consequence comprehension, is where these processes are most active. The prefrontal cortex, which usually reaches full maturity at age 25, is the last part of the brain¹² 

Using cannabis in adolescence can have major effects on three important brain areas:

• Prefrontal cortex: An area that continues to develop throughout adolescence and is essential for executive functions.¹¹ By interfering with its maturity, cannabis usage may have an impact on impulse control and decision-making
• Hippocampus: A component of the limbic system, which matures before the prefrontal cortex, the hippocampus plays a role in memory formation and learning¹¹
• Amygdala: This area, which processes emotions and fear responses, is a component of the limbic system that adolescents rely on to make decisions before the prefrontal cortex fully develops¹³ 

Adolescents exhibit heightened vulnerability to the effects of cannabis due to several developmental factors. Primarily, the adolescent brain is still undergoing significant development, making it more susceptible to external influences such as cannabis exposure.¹⁴ During this critical period, the brain experiences substantial neurodevelopmental changes, including synaptic pruning and myelination, these are essential for cognitive maturation and efficient neural connectivity.¹⁵ Different brain regions mature non-simultaneously, which is a noteworthy feature of adolescent brain development. The limbic system, which processes emotions and rewards, develops before the prefrontal cortex, which controls executive skills like impulse control and decision-making.^5,11 Because of this imbalance, teenagers may be more susceptible to the psychoactive effects of cannabis due to increased risk-taking behaviours and heightened emotional sensitivity.¹⁶ 

Additionally, the high adaptability of the adolescent brain makes it possible for quick learning and adaptation, but it also makes it more vulnerable to potentially dangerous chemicals like cannabis,¹⁷ because of its malleability. Cannabis use during adolescence can interfere with typical developmental paths and result in long-term behavioural and cognitive problems.^5,18

Long-term mental health effects

Adolescent cannabis use has been associated with a higher risk of psychotic illnesses, such as schizophrenia.¹⁹ Those who begin using cannabis earlier in life and use it more regularly have a higher risk of developing schizophrenia. Increased frequency and potency of cannabis usage are associated with an increased incidence of psychotic symptoms; this association seems to be dose-dependent.²⁰

Risk of psychosis

According to studies, smoking cannabis can cause acute psychosis in certain teenagers, which frequently reoccurs if the teen uses cannabis again after the initial psychotic episode has passed.²¹ The long-term symptoms linked to chronic cannabis use may be explained by the significant negative effects of THC on the large-scale alterations in neuronal connections that occur during adolescence.⁵

Anxiety and depression

Frequent cannabis use during adolescence has been linked to a higher chance of suicidal thoughts, feelings, and depression in later life. According to a meta-analysis of 11 studies with 23,317 participants, Adolescent cannabis use was associated with an increased risk of depression and suicidal conduct in young adulthood, even in the absence of a pre-existing disease.²² It is important to note that there is a complicated link between cannabis use and mental health problems. According to some research, youths who are depressed or have suicide thoughts may turn to cannabis as a coping mechanism, yet consuming cannabis might exacerbate both depressive and suicidal symptoms at the same time.⁴

Chronic cannabis usage during adolescence has been linked to cognitive deficits, especially in domains like memory, attention, and learning. Regular cannabis usage before the age of 18 was linked to a loss of 5 to 8 IQ points at a 20-year follow-up, according to a prospective research conducted in New Zealand.⁵ These findings showed that regular cannabis use hampered academic functioning and subsequent socioeconomic levels, although a subsequent twin research did not support them.²³

Long-term cannabis use in adolescence can cause issues with memory, learning, focus, attention, and problem-solving. These cognitive deficits may limit a person's future chances and development by having long-lasting effects on their academic and professional performance.²⁴

Long-term cannabis use may lead to a loss of motivation and ambition, a concept known as "amotivational syndrome." While this theory is still debated, studies have shown that frequent users often experience changes in behaviour.²⁵ Research also shows that when teens start smoking or vaping cannabis three to four times a week, their school performance tends to decline, and cannabis use can begin to take over their lives.

Short-term use has also been linked to issues like skipping school, getting low grades, and running into legal trouble. These problems can have lasting effects and may prevent young people from reaching their full potential as adults.²⁷

Preventive measures

Adopting efficient measures that reduce the possible detrimental effects of cannabis on youth is essential as the drug becomes more widely available as a result of legalisation and shifting public perceptions. The use of cannabis by teenagers is a growing problem, and this article examines several interventions and preventative strategies. In these initiatives, parents are essential because they set clear expectations and have open conversations with their children about the dangers of cannabis usage. Resources like simulators and conversations about family norms can provide teenagers with the skills they need to defy peer pressure and make sound decisions. Adolescent cannabis usage must be discouraged by policy measures. Youth access to cannabis can be greatly decreased by enforcing age restrictions, reducing THC potency, and regulating the sale and promotion of cannabis products.²⁸ By establishing these rules, legislators can aid in preventing cannabis usage at a young age.

Communities, schools, and medical professionals play a critical role in reducing teen cannabis usage. By including substance use education into the curriculum, school-based prevention initiatives can inform students about the dangers of cannabis usage. During regular check-ups, doctors can help spot early signs of cannabis use and offer helpful advice to both teenagers and their families. At the same time, community programs can support healthy choices by encouraging teens to take part in positive, engaging activities in a safe and supportive environment. Adolescents who participate in positive extracurricular activities can feel more purposeful and are less likely to abuse drugs.²⁹ Local community groups can also help support laws that make it harder for young people to get cannabis and promote proven ways to prevent its use. Intervention programs can help teenagers build resilience against peer pressure and other risk factors while also halting the generational transfer of substance use behaviours.

Summary

In summary, a comprehensive strategy is needed to safeguard teenage mental health in the age of legalized cannabis. To reduce young people's access to high-risk substances, policymakers must impose age restrictions and THC potency limits. Campaigns for public health education should focus on parents and teenagers to increase knowledge of the possible long-term consequences of cannabis usage. To better understand these hazards and create efficient preventative measures, more research is also necessary. We can better protect teenage mental health from the possible negative effects of cannabis use by striking a balance between legislation, education, and research initiatives.