Marijuanas Effects On the Brain & Body: Long And Short-Term Risks

Last Updated: December 24, 2020

Reviewed by Michael Espelin APRN

The popularity of marijuana is increasing for both medical and recreational use. With more states legalizing weed, the effects of marijuana might even be thought of as good. Despite its medical benefits for certain conditions, marijuana’s effects on a person’s body and brain can also be negative. This is especially true when considering teenagers who use or abuse cannabis, as it can negatively affect their brain development. Read further to learn about marijuana side effects.

Short-Term Marijuana Side Effects

No matter the reason pot is being consumed, and no matter how it is ingested, pot will have some effects. Marijuana effects on one’s health range from mild to severe and can vary depending on the strain of cannabis consumed and the product consumed (i.e., pills, oils, bud, or liquid marijuana drink). Depending on the strain, marijuana can show effects of a depressant or a stimulant. Before someone decides to use or not, they must weigh cannabis pros and cons. These can be divided into short-term and long-term side effects of weed.

Short-Term Marijuana Side Effects Are: 

  • Changes to the senses
  • Struggles with understanding the passage of time
  • Fatigue
  • Increased hunger
  • Mood fluctuations
  • Impaired motor skills
  • Difficulty with cognitive processes
  • Paranoia
  • Impaired memory
  • Increased heart rate
  • Blood vessel damage from smoke
  • Decreased blood pressure

Additionally, consuming cannabis in high doses can cause more dangerous marijuana side effects.

They Include:

Effects Of Weed On The Body

As marijuana recreational and medicinal use becomes legalized in many states in the U.S., more Americans are using the drug than ever before. This sudden shift in approach to weed has been polarizing. The population tends to divide itself into two camps: people who believe the effects pot has on the body to be purely beneficial and those who believe them to be strictly harmful.

However, the reality is more nuanced, with how marijuana affects the body being both good and bad depending on what systems an individual is looking at, the user’s age, how the drug is consumed, and the reason for use.

Cannabis Impact on the Respiratory System

If the method of ingesting the substance is smoking, the first system to experience effects is the respiratory system. It is a common misconception that marijuana smoke is less dangerous than tobacco smoke. In truth, marijuana smoke contains many chemicals and carcinogens similar to those delivered by tobacco smoke. This means the side effects of marijuana on the body can be similar to those of tobacco.

When ingested through methods other than smoking, it does not appear to impact the body’s respiratory health negatively.

Circulatory System

One of the more interesting interactions between marijuana and the body is its impacts on the circulatory—or cardiovascular—system. Because the circulatory system is responsible for getting the drug to the central nervous system, producing the high the drug is known for, it comes into direct contact with the drug soon after consumption, especially when smoked, vaped or used in the form of weed dabs. In new or casual users, cannabis can increase heart rate and supine blood pressure and even cause marked orthostatic hypotension.

Man has cardiovascular problems after cannabis use.

Logically, one might assume that these effects become worse with frequent and prolonged use. Still, the opposite is true: the more someone uses the drug, the closer to normal their body’s cardiovascular system becomes, even moving in the opposite direction (i.e., lowering supine blood pressure). However, for people predisposed to heart disease and other heart conditions, there is no safe level of weed use as it has been linked to myocardial infarction in those with poor cardiovascular health. Even healthy people should take caution, putting off things such as strenuous exercise until the drug is gone from the body.

Digestive System

When marijuana is consumed via bowls, joints, or bongs, the impact on the body’s digestive tract is lesser than when consumed via drinks, edibles, pills, and tinctures. THC, in particular, interacts with gastrointestinal tract cannabinoid receptors. For people with certain diseases, this interaction is a positive one; cannabis has been found to have therapeutic use in treating inflammatory bowel disease, irritable bowel syndrome, and motility-related disorders. This is because activating cannabinoid receptors can relax the lower esophageal sphincter, inhibit acid secretion and motility, and stimulate the intestinal primary sensory neurons.

However, when consumed by someone not suffering from gastrointestinal disorders, marijuana can lead to problems. For example, its ability to reduce diarrhea from intestinal diseases can cause constipation in the bodies of healthy persons. As such, whether these effects are positive or negative depends on the individual.

Immune System

There is significant concern regarding the interplay between marijuana and the immune system. Because the immune system is essentially the guardian of the body, any positive or negative impact of marijuana on it will have far-reaching consequences. However, studies on the effects of weed on the immune system are limited.

One research conducted on patients with HIV or Hepatitis C with focus on specific elements of the immune system has shown that marijuana can help improve the immune response in the bodies of individuals studied. However, they do not provide an accurate picture of the impact on immunity in healthy individuals or even individuals with non-autoimmune diseases.

One concern is that cannabis can over-activate certain elements of the immune system, leading to autoimmune disorders. Others theorize that marijuana has the opposite effect in those without autoimmune diseases, weakening their body’s immune response rather than strengthening it. However, these are just ideas at this stage and have yet to be researched properly, giving us a limited understanding of marijuana before and after impacts on the immune system.

Endocrine System

Research on marijuana interactions with the endocrine system has been primarily limited to fertility. Marijuana’s effects on the body’s reproductive system have been studied heavily in animal test subjects but sparingly in humans. However, the results of the studies have been almost universally negative. Heavy and long-term use in men has been found to reduce plasma testosterone levels, retard sperm maturation, and increase the production of abnormal sperm—which could, in turn, lead to congenital disabilities and miscarriages.

Females have shown similar effects. Cannabis consumption has been found to interfere with the hypothalamic-pituitary-gonadal axis and delay ovulation through reduced hormone secretion. While there are some studies of women who have undergone tubal ligation that show neutral effects, no research has shown a positive impact of marijuana on the body’s reproductive system.

Skeletal System

How marijuana affects health is so far-reaching, it even has an impact on the bones. However, this is the one body system where the impacts of marijuana have been found to be universally positive—at least for now. The CB1 receptor is found in skeletal nerve terminals while CB2 expresses in osteoblasts and osteoclasts, stimulating bone formation and inhibiting reabsorption. However, the studies on this are limited, and new studies may reveal more negative effects on the bones than positive ones.

Marijuana Side Effects on Brain

Cannabis can affect the brain in numerous ways, including by inhibiting short-term memories, distorting the sense of time, and regulating a person’s appetite. THC, the psychoactive compound found in marijuana, interacts with the body’s cannabinoid receptors. The chemical structure of THC is similar to the chemical in the brain called anandamide. The similarity causes the body to recognize THC and interact with the regular communication of the brain.

Doctor examining marijuanas effects on patient's brain.

After the user inhales the substance, the chemicals found in cannabis make their way into the bloodstream, which transports these different compounds throughout the body. 9-tetrahydrocannabinol, or THC for short, is a mind-altering chemical considered the most important component of all cannabis strains.

Additionally, marijuana also contains molecules that resemble those produced in the brain called cannabinoids. Once THC reaches the brain, it is picked up by the cannabinoid receptors, which are directly affected by the chemical.

Marijuana’s Effects On the Brain Are the Following: 

  • Short-term Memory Inhibition. One of the effects of weed on the brain is that long-term users may find it hard to recollect certain recent events. This is because marijuana has an inhibitory effect on the hippocampus, which is the part of the brain responsible for memory control. THC comes into contact with the hippocampus and disrupts its activity, leading to short-term memory problems
  • Distorted Sense of Time. One of the most highly-reported effects of marijuana is a distorted sense of time. This stems from marijuana's effect on the cerebellum and the altered blood flow to that part of the brain. The cerebellum is located in the lower back portion of the skull, which controls muscular activity, language, and the internal timing system
  • Appetite Increase. Whether one considers it a positive or negative effect, pot is known to cause a serious case of the munchies. How marijuana affects the brain lies in its effect on the hypothalamus—the brain's part in charge of regulating appetite. Subsequently, excessive eating after the consumption of a joint should not come as a surprise to experienced users. However, the way of consumption largely affects the chances of munchies
  • Drowsiness. One of the short-term marijuana side effects is feeling drowsy. Pot has an impact on CB1 Cannabinoid receptors in the brain, leading to an induction of sleep. The THC is what causes a feeling of drowsiness
  • Coordination and Reaction. Pot can negatively influence both the coordination and reaction time reaction times of its user. This is because THC influences both the cerebellum and basal ganglia, meaning the brain's signals are similarly influenced like they are when drunk. This is the reason why driving under the influence of marijuana is also prohibited. THC makes the user clumsier in every aspect, with walking and talking correctly becoming just as arduous. Studies also found that pot users were unaware of their clumsiness and errors made whilst under the influence. They also had a worse memory

Does Weed Kill Brain Cells?

Evidence shows that alcohol kills the cells of the brain, but does smoking weed kill brain cells? Even though pot affects the brain, it does not kill brain cells. However, marijuana brain damage can occur indirectly. THC affects the cells of the nerve in different regions of the brain. As a result, cannabis concentrate, such as wax marijuana, which is known to have high THC alters the brain’s mental and bodily functions.

Dangers Of Long-Term Use

A growing number of studies in humans and substantial evidence from animal research show the long-term effects of marijuana. Though cannabis use doesn’t seem to cause any structural damage, weed overdose can reduce mental focus and flexibility over time. In Pot’s long-term effects on the brain are:

Decline in IQ

Smoking pot can permanently lower IQ. This is one of the most dangerous effects of marijuana on teens as they tend to have a deficit in concentration, memory, and overall IQ.

Addiction

The development of problem use, which can also be called marijuana use disorder, is one of marijuana’s effects on the brain. In severe cases, it takes the form of addiction. When a person cannot stop using cannabis even though it negatively affects their life, addiction steps in. The brain’s reward system is a group of neural structures responsible for emotions and pleasure. Weed activates it by reinforcing stimuli and causing disorder, which results in addiction.

Mental health risks

The use of the drug carries mental health risks, and some studies show the link between marijuana and mental health. A person who starts using pot at an early age is more likely to experience mental health problems. Some of the mental health problems that can result from dope use are depression, anxiety, bipolar disorder, and schizophrenia.

Other Long-Term Effects Of Weed Are:

  • Lung disease and disorders, when cannabis is smoked
  • Lowered immune system
  • Reduction in long-term memory
  • Decreased testosterone
  • Irregular periods
  • Lowered fertility
  • Suicidal thoughts
  • Depression
  • Anxiety
  • An altered reward system in the brain, making further drug abuse more likely

The Risks of Street Cannabis

The negative effects of weed listed above can occur with the consumption of any type of pot from any source. However, there are increased risks when the pot is purchased from dealers rather than authorized dispensaries in states where it is legal.

Drug addict buying street cannabis.

The negative effects of weed when consumed illegally expand to include any other drugs handled in the same space, as there is a high risk of intentional and unintentional cross-contamination. The drug may also contain things such as pesticides, heavy metals, and mold.

Variables That Impact Side Effect Emergence

How marijuana affects your body will vary. Not everyone who uses cannabis will experience the same side effects. There are many variables at play that determine exactly how marijuana side effects will emerge in each person.

Some Of the Most Important To Consider Are:

  • The age of the user—the younger the user, the worse the long-term side effects
  • The strain of cannabis consumed—some are stronger and more psychoactive than others
  • How the weed was cultivated—different techniques produce different results
  • The method of ingestion—edibles have a faster and more lasting onset than smoking, and marijuana dabs are extremely potent
  • The presence of THC—not all cannabis products have THC, which is the psychoactive element in cannabis
  • The source of the product—authorized dispensaries tend to offer products with precise side effects, while street purchases are uncontrolled
  • The tolerance of the individual—some people experience effects faster and stronger than others
  • The frequency of use—the more often pot is used, the more likely it is that long-term side effects will develop

Does Smoking Weed Cause Cancer?

Legal medical and recreational use of marijuana is new to the United States, and as a result, research on the effects of marijuana is just starting to pick up. Due to the limited data available, there is no consensus within the medical community about whether weed can cause cancer. So, does that mean there is no worry about weed and cancer?

According to the data that is available, no. While links between cannabis and cancer, in general, are not strong, links between lung cancer and smoking cannabis have been observed. This connection is logical given that smoking other substances is known to cause lung cancer as well, and marijuana carcinogens are no less dangerous. For example, tobacco smoke has long been proven to cause lung cancer. As such, joints and marijuana bongs present greater risk than oils and edibles based on current research.

A False Sense of Security

This might sound like consuming weed in ways other than smoking is safe, but this is not necessarily true. At this point, research into things like oils, edibles, topicals, and marijuana drinks is minimal. This means that while there is no proof that these cannabis products can cause the disease, there is no definitive proof that they do not.

For example, small studies have found that men who used cannabis in any form had higher rates of testicular cancer. However, due to the small sample size and limited research, it is unclear if this is a matter of correlation or causation. Smoking pot and lung cancer may be the only proven link, but there could be more yet to be discovered. Scientists have a ways to go before they know for sure.

Effects Of Marijuana On the Teenage Brain

The fact that cannabis is a natural plant makes many teenagers who dab marijuana think it is a safe drug to smoke. Yet, studies have revealed marijuana for kids can be exceptionally harmful, and teens are especially prone to experience adverse effects when they turn toward experimenting with this plant. It is important to realize there are many other illicit drugs that are also made from plant-based materials yet pose significant threats to the user’s health.

Teens smoking weed have been found to experience a significant reduction in their performance at school, and then there are the effects that the substance has on the brain of a teenager that are negative as well.

Teenagers smoking weed.

An important factor that needs to be understood when discussing the marijuana teenage brain effects is that the substance tends to cause dependence. Many reports claimed pot is not, yet several studies have documented signs of addiction and dependence among frequent users.

The use of marijuana may lead to compulsive behavior and cause an adolescent to experience withdrawal symptoms when they cannot get their hands on the plant. The same study also reports recent statistics showed that 3% of the American population might already be experiencing signs of dependence on weed.

The same publication also states a teenager is up to four times at a higher risk when exposed to cannabis to develop a dependency on the drug, compared to being exposed to the substance for the first time as an adult.

A paper by the VA San Diego Healthcare System explains a dependency on weed can also make a teenager more likely to experience many adverse impacts on their life in general and complications in their future. In particular, the research explains that teens are likely to experience reduced school performance, with lower grades than before, if they start to utilize the substance.

Some studies have also noted teens who abuse pot are more likely to want to start experimenting with stronger drugs and other types of illicit drugs. This, in turn, can make a person go from smoking a joint now-and-then toward becoming a drug addict that uses cocaine, heroin, and other classes of harmful substances that may cause their bodies and brain psychological and physiological trauma.

Another important fact to consider in terms of marijuana use among teenagers and the effects the substance can have on their brain is that these individuals have a much greater risk of developing certain mental disorders later in their lives. Particularly, pot during adolescence has been associated with a higher likeliness of developing anxiety disorders and becoming depressed later on. These are mental health conditions that have adverse effects on the brain and can dramatically impact the individual’s life.

Marijuana Use Among Teens

Over the last decade, statistics on teenagers smoking marijuana slowly increased. The latest statistics on teen marijuana use announced by the National Institute on Drug Abuse for Teens report as much as 15.2% of 8th graders have tried marijuana before, with approximately 1.30% of 8th graders using it daily. The statistics tend to increase significantly among 10th and 12th graders. At the age of grade 12, about 44% of teens have experimented with the drug at least once in their lifetime. About 22.3% of 12th graders reported using marijuana on a monthly basis, with 6.4% of the 12th graders being daily smokers.

Getting Help With Weed Adverse Reactions

Ultimately, if the side effects of pot use are unable to be managed, the best option is to stop the use of the drug completely. In fact, unless someone is directed to use cannabis for medicinal purposes, eliminating use is recommended for both medical and legal reasons. The dangers of marijuana are great enough to avoid the drug and seek help in managing weed withdrawal symptoms.

For individuals already using marijuana and concerned about the potential negative health impacts on their bodies, treatment for substance addicts can help. There are rehabilitation centers available across the United States offering data-backed approaches to getting clean. Both outpatient and inpatient rehabilitation institutions can be used. Rehab for drug abuse is available in every state in the U.S., so there is always an option nearby. Do not be afraid to seek help.


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Published on: December 7th, 2016

Updated on: December 24th, 2020

About Author

Peter J. Grinspoon, MD

Dr. Peter Grinspoon is an experienced physician with long-term clinical practice experience. As a former analgesic addict, Dr. Grinspoon knows precisely how important it is to provide patients with effective treatment and support. Medical writing for him is the way to communicate with people and inform them about their health.

Medically Reviewed by

Michael Espelin APRN

8 years of nursing experience in wide variety of behavioral and addition settings that include adult inpatient and outpatient mental health services with substance use disorders, and geriatric long-term care and hospice care.  He has a particular interest in psychopharmacology, nutritional psychiatry, and alternative treatment options involving particular vitamins, dietary supplements, and administering auricular acupuncture.