What are the Effects of Marijuana on the Brain

Effects of marijuana on the brain. Recreational marijuana use is steadily rising, and along with it, so is the number of people dismissing the plant’s potential harm. The mind-altering chemicals in the marijuana plant pass from the bloodstream to the brain and affect the cognition, memory, learning, coordination, and pose a risk for developing serious mental disorders.

Effects of Marijuana on the Brain
Effects of Marijuana on the Brain

What is Marijuana?

Marijuana, also called cannabis, “pot,” or “weed,” is the dried leaves, flowers, stems, or seeds from the Cannabis sativa or Cannabis indica plant. Over 120 diverse chemical compounds reside within the plant—the most common being cannabidiol (CBD) and the psychoactive component, tetrahydrocannabinol (THC). THC is the main substance in marijuana that classifies it as a drug. Different parts of the plant have varying levels of chemicals. For example, flowers range from 5 to 20 percent THC.

Marijuana is used in the following ways:

  • Inhalation: Rolled and smoked like a cigarette (joint) or cigar (blunt), smoked in a pipe dry, water bong
  • Orally: Edibles, mixed into food, brewed into tea, capsules
  • Sublingual: Tinctures, dissolvable strips, sprays, or lozenges that are placed under the tongue or in the mouth
  • Topical: Lotions, oils, bath salts and salves absorbed through the skin

How Endocannabinoids Work

The endocannabinoid system is a biological system to maintain homeostasis. For the body to function properly, its conditions require balance. The heart rate must be within normal limits, temperature cannot be too hot or cold, and more. Cells in the body naturally produce endocannabinoids, which communicate with the nervous system and perform this role. Endocannabinoids attach to cannabinoid receptors on the surface of cells and are eventually destroyed by metabolic enzymes.
Marijuana, however, interferes with the endocannabinoid system. Cannabinoids from marijuana like THC bind to cannabinoid receptors, overloading the system and preventing naturally produced endocannabinoids from their regular tasks.

Marijuana’s Effects on the Body

The “high” marijuana induces effects a vast number of processes controlled by the endocannabinoid system—immune function, digestion, appetite, motor control, reproduction, mood, inflammation, memory, temperature regulation, pain to name a few. Physical effects on the body can be:

  • Rapid heart rate
  • Low blood pressure
  • Nausea
  • Increased appetite
  • Faster respirations
  • Sedation
  • Sexual problems
  • Relaxation
  • Increased risk of stroke

Effects of Marijuana on the Brain: The Brain’s Reward System

The reward system consists of a series of brain structures from the ventral tegmental area to the hypothalamus that mediates reward. Neurons in these brain areas release dopamine upon pleasurable behaviors such as food or sex. Marijuana acts on the brain’s reward system. As the THC attaches to cannabinoid receptors, the reward system is activated, and the user no longer responds as strongly to other pleasurable experiences. This is evidence of the addictive nature of marijuana.
Scientists have taken a recent interest in how marijuana interacts with the brain’s reward system. Published in the journal, Human Brain Mapping, long-term marijuana users had more activity in the reward system on magnetic resonance imaging when shown marijuana related objects than non-users, and they had a reduction of brain stimulation when given alternative cues like their favorite fruit.

Effects of Marijuana on the Brain: Memory Problems

The concept of memory is how humans classify experiences. Through memory, we encode, store, and recall information. These experiences drive our behavior. Memory is either short-term memory, which stores several items of information for mere minutes, or long term memory that remains indefinitely.

Marijuana alters the hippocampus—the part of the brain responsible for processing information and creating memories. THC prompts two physiological changes in the brain that affect memory. Firstly, experts link marijuana to a loss of brain cells. Imaging studies conducted with marijuana users depicted shrinkage of the brain’s gray matter over time. Gray matter is home to the brain’s neurons. Marijuana accelerates deterioration of neurons in the hippocampus.

Not only do the brain cells in the hippocampus die off, but they also weaken in connectivity. Hippocampal neurons do not communicate with the nervous system effectively when under the influence of marijuana.

Studies prove marijuana has little effect on long term memory, but smokers struggled with short term memory tests on recall. Aside from recall difficulties, marijuana prevents the formation of new memories while high and for a significant duration after the high wears off.

Effects of Marijuana on the Brain: Cognitive Dysfunction and Learning

Along with memory, marijuana’s effects on the brain precipitate cognitive dysfunction. The THC in marijuana prevents sustained attention and concentration. Its chemicals disrupt the frontal lobe, limiting one’s decision making abilities because they are unable to weigh the consequences of their actions. The cognitive effects of marijuana are especially detrimental to school and work activities, as learning new information is challenging, concentrating on tasks is complicated, and memory interferes with recalling details. THC levels in the specific marijuana strain determined the severity and length of these impairments.

The cognitive effects of marijuana are a recent subject of intrigue in the scientific community. Investigators revealed that chronic marijuana users who were abstinent for the study had inattention and impaired information processing that resolved after smoking, linking the substance to cognitive dysfunction (Devere, 2015). The tests uncovered marijuana had no impact on impulsivity and verbal fluency, however.

Effects of Marijuana on the Brain: Marijuana as An Appetite Stimulant

A journal article in Nature Neuroscience explains, “THC fits into the brain’s olfactory bulb, significantly increasing the animals’ ability to smell food and leading them to eat more of it.” This helps support the mechanism behind marijuana as an appetite stimulant. Cookies, a burger, endless amounts of potato chips—the insatiable post-high “munchies” are partly due to enhanced sensitivity to scents, which in turn, heightens the taste of food. Changes to the olfactory bulb convince the brain that it is starving, motivating food consumption. As endocannabinoid bind to the appropriate receptors, it triggers cells to release hormones (i.e. ghrelin, leptin, etc.) which regulate appetite.

Marijuana as An Appetite Stimulant
Marijuana as An Appetite Stimulant

Effects of Marijuana on the Brain: Coordination

In addition to appetite stimulation, marijuana endocannabinoids bind to nerve cells in the basal ganglia and cerebellum, which are responsible for motor movements. Marijuana causes imbalance, poor coordination, and delayed reflex response. Impaired motor coordination can make driving and physical activities dangerous.

Signs of poor motor function are:

  • Vertigo
  • Dizziness or feeling lightheaded
  • Loss of balance
  • Clumsiness
  • Gait changes
  • Fainting

Effects of Marijuana on the Brain: Mood Disruption

While marijuana is associated with feelings of stress-free relaxation, it impacts emotional processing because of its effect on neurotransmitters. Neurotransmitters are chemical messengers released by the brain’s neurons. They communicate to structures of the body and play an immense role in mood. Marijuana stimulates the release of dopamine, GABA, and serotonin to create a sense of euphoria. Afterwards, the brains serotonin levels are depleted. Alterations in these brain chemicals leave one alternating from depression to mania, paranoid to carefree, and many emotions in between. Age, frequency of use, the amount, and length of time of total use determines the extent marijuana has on the user’s mood.

Mental Disorders

Can marijuana cause mental illness? Marijuana use is higher amongst populations with mental illness. However, the exact link is unclear. Researchers are unsure if those with mental illness gravitate towards marijuana as a coping tool or if the drug is a direct cause. Regardless, marijuana increases the risk of developing a mental health disorder.

Psychosis and Schizophrenia

Psychosis is defined as a disconnection from reality. When someone has psychosis, the brain does not accurately process information. Hallucinating, seeing or hearing things that are not there, is a symptom of psychosis. It further leads to delusions—a persistently held false belief despite evidence that proves otherwise.

Although marijuana often triggers psychosis without the presence of an existing mental disorder, psychosis occurring with emotional problems and distorted thinking is characterized as the mental disorder schizophrenia. Marijuana exacerbates the symptoms of schizophrenia. According to the Schizophrenia Bulletin, it also provokes psychotic episodes as soon as 2 to 6 years earlier.


Marijuana heightens both positive and negative emotions experienced in the moment. In anxious individuals with persistent, excessive worry common of anxiety disorders, marijuana can be counterproductive. Studies at Georgetown University (Carvalho, 2012) found that the initial increase in GABA and serotonin with marijuana use inhibits norepinephrine, a neurotransmitter controlling alertness and anxiety. For those with anxiety, decreased norepinephrine arouses activity in the brainstem and limbic forebrain. They experience a rebound effect with symptoms such as fear, panic attacks, and paranoia.


Depression is a mood disorder distinguishable by persistent sadness occurring longer than two weeks, feelings of hopelessness, a loss of interest in usual activities, apathy, and sleep disturbances. Marijuana substantially increases the risk of depression. A cohort study of adolescents revealed that weekly recreational use of marijuana doubles the risk of developing depression later in life. Marijuana hinders regular emotion, creating the illusion that users have a reprieve from their symptoms. However, as the effects of the drug subside, emotions return with vengeance.

Marijuana and the Adolescent Brain

The consequences of marijuana are more profound for adolescents than for adults. Adolescence is a developmental stage marked by vital changes in the brain’s wiring. The body’s natural endocannabinoids rewire the brain to efficiently maintain homeostasis during growth. In adolescence, appetite picks up, sleep schedules lengthen, emotions are sensitive—the body’s endocannabinoids are undergoing serious adjustments. Marijuana interferes with the endocannabinoid system when it is most vulnerable, leaving younger populations to encounter the drug’s side effects on a larger scale. IQ and learning are most severe. Frequent marijuana use in adolescence results in an IQ score decreased at an average of 5.8 points by adulthood, whereas non-users gained 0.8 points (Meier, Caspi, et al., 2012). Teens are no experts in emotional control. Thus, they are 7 times more likely to commit suicide as a result of marijuana’s mental health repercussions. When the brain does not have the opportunity to fully develop, the effects of marijuana on the brain are potentially permanent.


Carvalho, A. F., & Van Bockstaele, E. J. (2012). Cannabinoid modulation of noradrenergic circuits: implications for psychiatric disorders. Progress in neuro-psychopharmacology & biological psychiatry, 38(1), 59–67. doi:10.1016/j.pnpbp.2012.01.008

Crean, R. D., Crane, N. A., & Mason, B. J. (2011). An evidence based review of acute and long-term effects of cannabis use on executive cognitive functions. Journal of addiction medicine5(1), 1–8. doi:10.1097/ADM.0b013e31820c23fa

Devere, R. (2015). Recreational Marijuana and Cognitive Decline: What Every Clinical Neurologist Needs To Know. Retrieved from https://practicalneurology.com/articles/2015-oct/recreational-marijuana-and-cognitive-decline-what-every-clinical-neurologist-needs-to-know

Meier, M.H., Caspi, A., Ambler, A. Harrington, H. Houts, R., Keefe, R.S., McDonald, K., Ward, A., Poulton, R., & Moffitt, T.E. Cannabis use and neuropsychological decline. Proceedings of the National Academy of Sciences Oct 2012, 109 (40) E2657-E2664; DOI: 10.1073/pnas.1206820109

National Survey on Drug Use and Johnston L, O’Malley P, Miech R, Bachman J, Schulenberg J. Monitoring the Future National Survey Results on Drug Use: 1975-2015: Overview: Key Findings on Adolescent Drug Use. Ann Arbor, MI: Institute for Social Research, The University of Michigan; 2015.

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