How Marijuana Affects the Mind & Body

Written by Melissa Carmona

& Medically Reviewed by Benjamin Caleb Williams, RN

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Last Updated - 04/05/2023

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Updated 04/05/2023

Marijuana is a popular drug that over 48 million people in the United States use each month. Marijuana’s popularity is due, in part, to the misconception that it does not create any negative effects. Unfortunately, marijuana has many potentially negative effects on the body and mind that people should be aware of before using it.

Short-Term Effects of Marijuana

The interactions tetrahydrocannabinol (THC) has with cannabinoid receptors in the brain lead to marijuana’s side effects.

These may include: 

  • Altered senses
  • Altered sense of time
  • Mood changes
  • Impaired body movement and memory
  • Cognition and problem-solving difficulties
  • Hallucinations
  • Delusions
  • Psychosis

The short-term effects of marijuana can begin within minutes after being inhaled but may take 30–60 minutes when ingested. Marijuana’s effects will typically last about 4–6 hours but may last longer if ingested.

While many people report having an enjoyable experience with light and infrequent marijuana use, people who use large or concentrated amounts or who have not used marijuana before may experience anxiety, panic attacks and paranoia. Using marijuana may also trigger underlying psychiatric diseases that were not previously causing significant symptoms.

Side Effects of Medical Marijuana

Most people who use marijuana only use it infrequently and in small doses.

The symptoms that these individuals most commonly experience are:

  • Rapid heart rate
  • Dry mouth
  • Reddened eyes
  • Decreased concentration
  • Changes in the sense of time
  • Decreased coordination
  • Decreased depth perception

Less common but more severe side effects may include:

  • Severe nausea
  • Hallucinations
  • Depression
  • Panic attacks
  • Fainting

While marijuana side effects are not often harmful, these side effects can lead to an increased risk of injuries. Impaired coordination, changes in judgment, decreased reaction time, and other changes that occur can make activities like driving or crossing the road dangerous.

How Marijuana Affects the Brain

Marijuana directly interacts with receptors in the brain, changing how it works and potentially having a lifelong impact on brain function. The brain is constantly developing and changes from birth until someone’s late teens to early twenties. Marijuana effects are especially impactful while the brain is still developing.

How Marijuana Affects the Adult Brain

While marijuana does impact the adult brain as much as other stronger substances, it still influences the brain and causes addiction. Research shows that one in ten adults who use marijuana will become addicted to it.

Addiction is related to the release of chemicals in the brain called endorphins after using marijuana. Endorphins create a sense of pleasure and are used by the brain to reinforce beneficial behaviors like eating, having intercourse, socializing and succeeding at difficult tasks. By artificially creating endorphins, the brain’s desire to use marijuana is reinforced, increasing the likelihood that it will be used again. This starts a cycle of continued use and further reinforcement, eventually becoming an addiction.

How Marijuana Affects the Developing Adolescent Brain

According to the CDC, marijuana specifically affects several parts of the brain.

In adolescents, this includes parts of the brain responsible for:

  • Memory
  • Learning
  • Attention
  • Decision-making
  • Coordination
  • Emotions
  • Reaction time

Studies have shown that marijuana use in adolescents can reduce IQ by up to 8 points.

The risk of addiction is also higher for adolescents than adults. About one in six adolescents using marijuana develop an addiction. The big difference is that teens’ brains are still developing. Changes in the brain during childhood affect that development, making addiction stronger and more difficult to overcome.

Other Effects of Marijuana Usage

While most people understand that marijuana use is potentially addictive and affects the way the brain works, there are many other important effects that people often fail to consider.

Breathing Problems

The THC in marijuana itself is not known to cause breathing problems. Smoking or vaping marijuana, however, can lead to serious long-term problems caused by introducing foreign substances into the lungs.

Effects of smoking or vaping marijuana may include:

  • Inflammation of the airways
  • Wheezing
  • Coughing
  • Increased phlegm

These effects can raise the risk of certain lung diseases, such as pneumonia. Additionally, vaping is a common but newer way of using marijuana. Due to its newness, there are likely long-term effects of vaping marijuana that have not been discovered yet.

Mental Effects

Marijuana use produces negative mental health effects in some individuals; this can include hallucinations, paranoia and anxiety. Marijuana is also thought to be connected with an increased risk of developing mental health diseases such as schizophrenia, although research in this area is still ongoing.

Marijuana is known to worsen existing mental health problems. Someone who has minor symptoms from a mental illness or is more predisposed to mental illness is more likely to have the mental health issue become more severe after using marijuana.

Effects on the Heart

Marijuana is known to create chest pain in people who use it at a higher frequency than other individuals. According to Harvard Health, this is because THC can make your heart pump harder and faster while also dilating your blood vessels. This could be dangerous in individuals who have any kind of underlying heart disease, but there is still ongoing research on exactly how dangerous it could be.

In addition to the effects of THC, smoking marijuana can also expose you to other chemicals used in marijuana cigarettes that may increase the risk of heart attacks and strokes.

Marijuana and Alcohol

Mixing alcohol and marijuana can lead to dangerous health situations and should be avoided.

Alcohol increases the effects of THC: if you use alcohol before using marijuana, the amount of THC that interacts with receptors in your brain will be higher. This creates a larger dose of marijuana, making the side effects more severe.

Using marijuana and then alcohol may increase the effects of intoxication, although there is not much research into this combination. Some research suggests that using marijuana before drinking alcohol can lead individuals to underestimate the effect alcohol is having on them.

Both marijuana and alcohol lead to changes in perception, response time and reflexes, making the combination of both of these drugs potentially dangerous.

Secondhand Effects of Marijuana

According to the CDC, marijuana contains many of the same cancer-causing chemicals that are in tobacco smoke. Exposure to these chemicals by being around smoking is known to cause cancer and increase the risk of other diseases.

Secondhand Smoke

The effects of secondhand marijuana smoke are not well studied or understood. It is thought that the THC in marijuana can affect others through secondhand marijuana smoke, but the effects of secondhand marijuana smoke specifically have not been well studied.

Children in the home are often the ones most at risk for secondhand smoke-related health problems. Many of the risks of secondhand tobacco smoke are likely similar to secondhand marijuana smoke.

Smoking Marijuana While Pregnant

Research into smoking marijuana while pregnant has found no impact on the baby’s likelihood of congenital diseases. However, it has been found marijuana use can lead to lower, unhealthy birth weight. Though no major risks have been proven for women who smoke marijuana while pregnant, there isn’t much research in this area, and experts still do not see it as safe.

Signs of Marijuana Use

Understanding the signs of marijuana use can help people recognize it in loved ones so they can support and help them get treatment.

Signs of marijuana use can include:

  • Red eyes
  • Seeming tired or lethargic
  • Coordination problems
  • Cravings for food
  • Confusion
  • Problems focusing
  • Being oddly talkative
  • Losing interest in typical activities
  • Being secretive

Other signs of marijuana use can include the presence of paraphernalia, such as marijuana leaf debris, rolling papers, eye droppers or pipes.

Is Marijuana Addictive?

Reputable medical sources, such as the CDC and the medically-respected Merck Manual, have found that marijuana addiction is definitely possible.

Ten signs of marijuana addiction include:

  • Developing a tolerance to the drug, meaning larger doses are needed to get the same effect
  • Using more marijuana than you expect or intend to
  • Trying to stop using marijuana and being unsuccessful
  • Continuing to use marijuana despite negative consequences
  • Putting a lot of focus on when you’ll get high next or spending the majority of your time high
  • Losing interest in other activities such as school or work
  • Declining performance at school, work or activities
  • Using marijuana as a way to self-medicate
  • Feeling like you have to use marijuana to feel normal or relaxed
  • Basing your schedule or life on whether or not you can get high

These aren’t the only signs of addiction to marijuana, but they are some of the most commonly recognized signs of marijuana addiction.

Can You Overdose on Marijuana?

Overdosing on marijuana is uncommon and rarely fatal, although the creation of more concentrated forms of marijuana and synthetic forms of marijuana are increasing marijuana’s overdose risks.

A marijuana overdose is most likely to occur in people who smoke concentrated THC. A marijuana overdose is also more common when using edibles, as edibles take longer to act. People using edibles for the first time, especially, may ingest a large amount in the half-hour it takes for the THC to begin to have an effect.

A marijuana overdose will typically cause stronger marijuana symptoms than normal. It may also cause an unpleasant sensation, sometimes called “greening out,” that causes nausea, dizziness and a feeling of terror and being unwell. Heavy marijuana use can also cause a condition called cannabinoid hyperemesis syndrome that causes severe vomiting for up to 48 hours.

Drug overdose can be fatal. If you suspect someone is experiencing an overdose, call 911 immediately. Do NOT be afraid to seek help. If you do not have access to a phone contact Colorado Poison Center for online assistance.


Centers for Disease Control and Prevention. “What We Know about Marijuana.” November 9, 2021. Accessed October 7, 2022.

O’Malley, Gerald & O’Malley, Rita. “Marijuana (Cannabis).” Merck Manuals. May, 2020. Accessed May 11, 2021.

Cunha, John. “Medical Marijuana (Cannabis).” RxList. Accessed May 11, 2021.

Lopez-Quintero, Catalina; Pérez de los Cobos, José; Hasin, Deborah S.; Okuda, Mayumi; Wang, Shuai; Grant, Bridget F.; & Blanco, Carlos. “Probability and predictors of transition[…] Conditions (NESARC).” Drug and Alcohol Dependence. December 8, 2010. Accessed May 11, 2021.

National Institute on Drug Abuse. “Is there a link between marijuana use an[…]ychiatric disorders?” April 13, 2021. Accessed May 11, 2021.

Ellgren, Maria. “Neurobiological Effects of Early Life Ca[…]e Gateway Hypothesis.” Karolnska Institutet. 2007. Accessed May 11, 2021.

Harvard Health. “Marijuana and heart health: What you need to know.” June 24, 2019. Accessed May 11, 2021.

Lukas, S. E.; Benedikt, R.; Mendelson, J. H.; Kouri, E.; Sholar, M.; Amass, L. “Marihuana attenuates the rise in plasma […]ls in human subjects.” Neuropsychopharmacology. August 1992. Accessed May 11, 2021.

Centers for Disease Control and Prevention. “Secondhand Marijuana Smoke.” October 19, 2020. October 7, 2022.

American Academy of Pediatrics. “The Dangers of Secondhand Smoke.” May 10, 2017. Accessed May 11, 2021.

Dysart, Kevin C. “Prenatal Drug Exposure.” Merck Manuals. March 2021. Accessed May 11, 2021.

Galli, Jonathan; Andari Sawaya, Ronald; Friedenberg, Frank. “Cannabinoid Hyperemesis Syndrome.” Current Drug Abuse Reviews, December 2011. Accessed May 11, 2021.


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