Effects of Marijuana on the Brain

Human Brain

Marijuana, also known as cannabis, can trigger a dopamine release in the brain that compels individuals to use it. However, cannabis use can also lead to negative effects on the brain, especially with long-term use. To better understand the nature of marijuana, it is important to understand its chief chemical component: THC.

Tetrahydrocannabinol (THC)

THC, also known as tetrahydrocannabinol, is a potent psychoactive chemical. According to the book Uppers, Downers, and All-Arounders, inside the brain there are neurotransmitter receptor sites designed to accept anandamide, a molecule naturally occurring in the body which is similar in structure to THC. It's so similar, in fact, that the brain can't tell the difference. When the THC fills these receptor sites instead, it overexcites the amygdala, the area of the brain that regulates emotions, appetite, learning, memory, and motor coordination.

Short-Term Effects

When marijuana is smoked, therefore bypassing the stomach and going straight into the bloodstream, it can quickly reach the brain, resulting in short-term feelings of relaxation or euphoria. The concentration of THC in the particular strain of marijuana and the amount of time the person inhales it will determine the intensity of these feelings.

According to the National Institute on Drug Abuse, within a few minutes of initial use, marijuana smokers are likely to experience one or more of the following symptoms:

  • A reduced ability to track objects, such as a moving car
  • Increased appetite or "munchies"
  • Difficulty concentrating or paying attention
  • Impaired judgment
  • Paranoia
  • Anxiety or depression

Many users find that even ordinary things suddenly become hilarious or very interesting as a result of these changes in perception.

Long-Term Effects

According to the National Council on Alcoholism and Drug Abuse, individuals who smoke three or more joints per week are considered heavy users. While the occasional user rarely experiences significant long-term effects, it's different for the chronic users. Since it can take as long as two weeks for the body to eliminate all the chemicals from one joint - depending on individual body chemistry - this habitual user remains almost constantly under the influence, which could lead to serious problems.

Memory Difficulties
According to the National Academy of Sciences, chronic marijuana use can lead to changes in the structure of the brain, which can cause a lifetime of impaired memory and learning. The hippocampus, the area of the brain responsible for storing short-term memory, expects to receive stimulation from anandamide. When it instead receives THC, it limits how much short-term memory is available for use and little to nothing gets stored. The degree of impairment increases if chronic use continues for three or more years.


According to Uppers, Downers and All-Arounders, tolerance often develops as a result of long-term marijuana use. Constant stimulation of the amygdala results in downregulation of neurotransmitter receptor sites. Some sites are shut down to prevent further overstimulation - whether naturally or from the drug. This is the body's way of protecting itself from overdose.

Due to this downregulation, the user has a decreased ability to experience normal feelings of relaxation or excitement in the absence of the drug. Things that seemed okay before the chronic use, such as sitting through a class session, now seem unbearably stressful or boring when not under the influence.

Schizophrenia Risk
Northwestern University reports a link between chronic marijuana use and schizophrenia. A 2013 study showed, "Of the 15 marijuana smokers who had schizophrenia in the study, 90 percent started heavily using the drug before they developed the mental disorder." This does not imply causation of the disorder, but it does imply that marijuana use increases the likelihood that individuals with a family history of schizophrenia will develop the disorder. No similar correlation is found with other common mental disorders, such as anxiety and depression.

Impaired Juvenile Brain Development

If a user starts smoking marijuana in adolescence, when the brain is still working to strengthen well-worn neural pathways and break those that are rarely used, the drug can be very detrimental. According to NPR, Madeline Meijer reported in a Duke University Study, "People who began using marijuana in their teenage years and then continued to use marijuana for many years lost about eight IQ points from childhood to adulthood."

While marijuana may not actually "kill brain cells," this study does show that the drug can cause changes in brain structure during these critical developing years.


Many marijuana users argue that cannabis is not addictive. Others say that while it is not physically addictive, it is psychologically addictive. Still others say that it is just as addictive as any other drug.

If you are struggling with your marijuana use, don't waste your time considering which of these arguments is the case. If your use is hindering your quality of life, it's a good idea to get help. Luckily, there are support groups nationwide that focus on cannabis addiction specifically, so assistance is not hard to find if you seek it out.

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Effects of Marijuana on the Brain