Sample Research Paper on Marijuana and Brain Development


There are many claims about marijuana’s benefit to an individual’s mental health. Studies and anecdotes suggest that marijuana can be great for eating disorder patients and people with PTSD. These benefits come from the observation that chemicals in marijuana can alter brain processes. However, this brain altercation may also affect a marijuana user’s brain development. Marijuana use can lead to lower intelligence, executive function impairment, and brain matter damage which are detrimental to brain development.

Marijuana-Related Animal Testing

The legal issues of marijuana make research and clinical studies about the topic complicated. Many researchers tend to use existing data on marijuana-related questions or utilize alternative subjects to get around legal limitations. In the research regarding marijuana and brain development, this issue becomes more significant since researchers cannot test an illegal substance on live human brains. As an alternative, researchers test marijuana-related chemicals in animal brains to assess its effects.

These animal studies found that marijuana consumption can have adverse long-term effects on the brain. Rats developed problems with learning, memory, and other cognitive impairments. Marijuana did not only cause functional impairments but also structural changes in the brain (NIDA, 2021). These problems occurred at different stages in the rats’ lifespan, indicating that marijuana changes how the brain and its specific parts develop. The study also showed that marijuana consumption at the adolescent age increases the risk of using other drugs which can then worsen the effect of the substance on brain development.

Marijuana’s Effects on Brain Development

Most studies on marijuana suggest that the substance has a detrimental effect on the human brain. It can cause a drop in IQ points, impair executive functions, and damage the structure of the brain (NIDA, 2021; Schmidt, 2021; Weiland et al. 2015; Weir, 2015). However, some studies suggest that marijuana use can provide benefits for mental health patients (Pryor, n.d.; Rodriguez, 2021). These conflicting studies show the gap in marijuana research, especially in its long-term effects, and imply the need for more clinical studies. With this in mind, individuals should approach marijuana research as a developing field.

Lower Intelligence

Low intelligence is a significant adverse effect of marijuana on the brain. Lifetime exposure to the substance can cause an individual to have lower scores on verbal memory tests (Volkow et al., 2016, cited in NIDA, 2021). This type of test assesses an individual’s ability to memorize words and lower test scores may suggest problems with learning and memory. Furthermore, other studies showed that persistent marijuana users can experience a loss in their IQ points as they continue using the substance (Meier et al., 2012; NIDA, 2021). Marijuana users can lose an average of six to eight points, illustrating a significant and harmful effect. The loss of IQ points may imply damage to the brain and as an individual’s brain continues to develop, this can lead to more adverse effects.

However, not all studies regarding marijuana and loss of IQ points have the same results. Other studies report that other factors, such as genetics and social environment, can contribute to the loss of IQ points in marijuana users (cited in NIDA, 2021). Since some of the studies fail to take into account other factors or are just unaware of a subject’s specific background, the results vary. As mentioned earlier, there is an issue in marijuana research and the legal limitations prevent researchers from conducting intensive studies.

Executive Function Impairment

Another significant effect of marijuana on the brain is executive function impairment. These effects, however, are short-term and often disappear when the “high” from marijuana dissipates Weir, 2015). Executive functions relate to an individual’s attention, memory, learning, and decision-making. Impairment in these functions means that an individual will not be able to function normally and efficiently. While short-term effects may not directly affect brain development, this can still have lasting detrimental effects; especially on younger individuals with susceptible developing brains. This is especially true for children, who may accidentally consume THC from secondhand marijuana smoke.

There was also a study that observed differences between the prefrontal cortex of marijuana users and non-users. The study found that marijuana users’ prefrontal cortex has sped-up thinning compared to non-users (Schmidt, 2021). Thinning of the prefrontal cortex is natural and occurs as the brain develops. According to the researchers, early thinning of the prefrontal cortex can lead to long-term behavioral and memory problems (Schmidt, 2021). Additionally, the researchers also noted that the study does not prove that marijuana causes early thinning but only that the substance affects brain development. This is because of other factors that may contribute to the thinning aside from marijuana. Still, the results suggest that marijuana can directly or indirectly affect executive functions.

Brain Matter Damage

Marijuana use can also lead to damage to the brain’s white matter. Gruber (2013) conducted a study that revealed white matter damage in the brains of heavy marijuana users (cited in Weir, 2015). White brain matter is essential to ensure healthy communications among neurons and impulse control. Damage to this part of the brain can lead to higher impulsivity, making it difficult for an individual to have self-control. As the brain develops, especially for young individuals, the damage can cause behavioral problems that will affect one’s personality.

Aside from white matter damage, marijuana can also affect gray matter. According to one study, marijuana users tend to have significant changes in gray matter density of the nucleus accumbens and amygdala. These two brain regions play a role in addiction since they are responsible for brain processes regarding motivation, pleasure, memory, emotion, and reward processing  (Journal of Neuroscience, 2014, cited in Weir, 2015). Changes in these parts of the brain can lead to developing addictive habits. Children and teens may develop poor decision-making skills and poor self-control which could affect their personal, academic, and future professional life.

Similar to other studies and marijuana-related topics, some studies produced contrasting results regarding marijuana and brain matter damage. Weiland et al. (2015) conducted a study that revealed that marijuana did not have any effect on gray matter density since it was alcohol intake that led to the changes. This study showed that marijuana’s effect on brain development is difficult to identify since there can be other factors that contribute to changes. Despite the result of this study, researchers cannot still rule out the possible effects of marijuana on brain development since marijuana-related factors, such as combinations of marijuana and other substances, may cause brain matter damage or changes.

Marijuana’s Effect Based on Gender

Studies have shown that marijuana can have different effects on gender. Some research suggests that adolescent females are more susceptible to marijuana’s effects than boys (Weir, 2015). This means that female children and adolescents may suffer more significant effects on brain development if they start using marijuana. This can affect their ability to learn and make decisions. Additionally, this gender-based difference may mean that marijuana users must regulate their substance consumption depending on their demographic.

Marijuana and the Adolescent Brain

Marijuana’s potential effects will be more evident in developing brains, such as the brain of children and adolescents. Various studies showed that marijuana use has stronger effects on the adolescent brain since most of the areas are still developing. This can lead to long-term structural changes that will affect various aspects of an adolescent’s life (Gruber, 2012; Martin-Santos et al., 2013, cited in Weir, 2015). Starting marijuana use at an early age will intensify these effects which can lead to bad academic performances and poor life choices.


Marijuana use can lower intelligence, impair executive function, and damage brain matter which can interfere with normal brain development. These changes are more evident in adolescents and individuals who use marijuana early in their life. Due to this, they can develop unhealthy behaviors and habits. They may have poor decision-making skills, impulse control, memory, and difficulty in learning. While many studies show that marijuana has negative effects, some studies suggest the contrary. There is a significant need for more marijuana-related research to better assess how the substance can affect brain development.

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Meier, M., Caspi, A., Ambler, A., & Moffitt, T. (2012). Persistent Cannabis Users Show Neuropsychological Decline from Childhood to Midlife. Psychological and Cognitive Sciences. Available at Accessed July 19, 2022.

NIDA (2021). What Are marijuana’s Long-Term Effects on the Brain? Available at Accessed July 19, 2022.

Pryor, T. (n.d.). Budding New Considerations about the Use of Cannabis in Eating Disorder Treatment. EDCare. Available at Accessed July 20, 2022.

Rodriguez Jr., I. (2021). Federal Study Finds Cannabis Beneficial for PTSD Treatment. Veterans of Foreign Wars. Available at Accessed July 20, 2022.

Schmidt, S. (2021). Cannabis May Alter a Teen’s Developing Brain. Science News for Students. Available at Accessed July 19, 2022.

Shen, H. (2020). Cannabis and the Adolescent Brain. PNAS. Available at . Accessed July 19, 2022.

Weiland, B., Thayer, R., Depue, B., Sabbineni, A., Bryan, A., & Hutchison, K. (2015). Daily Marijuana Use Is Not Associated with Brain Morphometric Measures in Adolescents or Adults. Journal of Neuroscience, vol 35(4). Available at Accessed July 19, 2022.

Weir, K. (2015). Marijuana and the Developing Brain. American Psychological Association, vol 46(10). Available at Accessed July 19, 2022.

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