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Health Effects

Learn more about how marijuana affects the brain and body.

Addiction

Some people think that marijuana is not truly “addictive” or that people can’t become “hooked” on the drug, but research shows that about 1 in 10 marijuana users will become addicted. For people who begin using before the age of 18, that number rises to 1 in 6.[1, 2, 3]

Some of the signs that someone might be addicted include:

  • Unsuccessful efforts to quit using marijuana.
  • Giving up important activities with friends and family in favor of using marijuana.
  • Using marijuana even when it is known that it causes problems fulfilling everyday jobs at home, school or work.[4]

People who are addicted to marijuana may also be at a higher risk of other negative consequences of using the drug, such as problems with attention, memory, and learning.

It is also important to be aware that the amount of tetrahydrocannabinol (THC) in marijuana (i.e., marijuana potency) has increased over the past few decades. The higher the THC content, the stronger the effects on the brain. In addition, newly popular methods of using marijuana (e.g., dabbing, edibles) may deliver very high levels of THC to the user.[5]

Researchers do not yet know the full extent of the consequences when the body and brain (especially the developing brain) are exposed to high concentrations of THC or how recent increases in potency affect the risk of someone becoming addicted.[5]

Brain Health

Marijuana use directly affects the brain — specifically the parts of the brain responsible for memory, learning, attention, decision making, coordination, emotions, and reaction time.[6, 7]

Short-term effects of marijuana on the brain

Heavy users of marijuana can have short-term problems with attention, memory, and learning, which can affect relationships and mood.

Long-term effects of marijuana on the brain

Marijuana also affects brain development. When marijuana users begin using as teenagers, the drug may reduce attention, memory, and learning functions and affect how the brain builds connections between the areas necessary for these functions.[6-8]

Marijuana’s effects on these abilities may last a long time or even be permanent. This means that someone who uses marijuana may not do as well in school and may have trouble remembering things.[6, 7]

The impact depends on many factors and is different for each person. It also depends on the amount of tetrahydrocannabinol (THC) in marijuana (i.e., marijuana potency), frequency, age of first use, and whether other substances (e.g., tobacco and alcohol) are used at the same time.

Marijuana and the developing brain

Developing brains, like those in babies and children, are especially susceptible to the adverse effects of marijuana. Although scientists are still learning about these effects of marijuana on the developing brain, studies show that marijuana use by mothers during pregnancy may be linked to problems with attention, memory, problem-solving skills, and behavior problems in their children.[8-12]

The Health Effects of cannabis and Cannabinoids. Current State of Evidence and Recommendations For Research

Cancer

There is mixed evidence about whether marijuana can cause cancer, partly because most people who use marijuana also use tobacco, a substance that does cause cancer.[13] Researchers have found an association between current, frequent, or chronic marijuana smoking and testicular cancer (non-seminoma-type).[15] More research is needed to understand the full impact of marijuana use on cancer.

Heart Health

The compounds in marijuana can affect the circulatory system and may increase the risk of heart attacks and strokes.

Studies have shown smoking marijuana can have a big effect on heart rate and blood pressure, including:

  • High heart rate and blood pressure.[16]
  • An increase in the report of chest pains when exercising among people with existing chest pain.[17]

Previous research has found a significant increase in the risk of heart attack in the hours after marijuana use.[18] Additional research is needed to confirm the total risk. Smoking marijuana can harm lung tissues and cause scarring and damage to small blood vessels. It could also lead to increased risk for stroke, mini-stroke, and heart disease.[19-23] More research is needed to understand the full impact of marijuana use on the circulatory system to determine if marijuana use leads to higher risk of death from these causes.

Lung Health

Smoke is harmful to lung health. Toxins and carcinogens are released when marijuana is burned. When these toxins and carcinogens are smoked, they are inhaled into the lungs, increasing health risks. Smoke from marijuana contains many of the same toxins, irritants, and carcinogens as tobacco smoke.[24, 25] Smoking marijuana can lead to a greater risk of bronchitis, cough, and phlegm production.[26-31] These symptoms generally improve when marijuana smokers quit.[32, 33]

Secondhand Marijuana Smoke

Secondhand marijuana smoke contains tetrahydrocannabinol (THC), the chemical responsible for most of marijuana’s psychological effects, and many of the same toxic compounds in smoked tobacco. Therefore, breathing it could affect the health and behavior of nonsmokers, including babies and children who are exposed.[28, 34, 35]

Mental Health

There is still a lot to learn about whether marijuana use may lead to mental health problems or if having a mental illness makes people more likely to use marijuana. And as with other drugs, factors like the age of users, how early they start, the amount of the drug they used, and their genetics all could make a difference in whether or not long-term problems develop.[42] But current research shows:

  • Marijuana users are significantly more likely than nonusers to develop chronic mental disorders, including schizophrenia. Schizophrenia is a type of mental illness where people might see or hear things that aren’t really there (hallucinations).
  • Some marijuana users have an increased risk for psychosis (loss of reality), a serious mental disorder where people have false thoughts (delusions).
  • Marijuana use has also been linked with depression and anxiety, and with suicidal thoughts among teens. However, it is not known whether this is a causal relationship or simply an association.
  • Marijuana use can trigger psychosis in people with schizophrenia.[39-41]

Poisoning

Eating foods or drinking beverages that contain marijuana have some different risks than smoking marijuana, including a greater risk of poisoning. These “edibles” are products such as cookies, sodas, brownies, and candies that have been made with THC—the active ingredient in marijuana.[43-46]

Unlike smoked marijuana, edibles can:

  • Take from 30 minutes to 2 hours to take effect.
  • Cause effects that last longer than expected depending on the amount, the last food eaten, and medications or alcohol used at the same time.

The amount of THC, the main psychoactive ingredient in marijuana, can vary in edible marijuana products. This makes it harder to control how much THC is consumed. For example, in states where recreational marijuana use is legal, one cookie or brownie might contain multiple “servings” in the product or package. That means a single marijuana cookie or brownie, or any other marijuana edible, might contain as much as 100 mg of THC. So if someone ate an entire cookie or brownie—each one a single “serving”—it would be like taking many hits of a marijuana cigarette at one time. The amount of THC in homemade marijuana edibles can vary even more. Many users can be caught off-guard by the stronger potency and long-lasting effects of edibles.[46, 47]

The effects of THC also take longer to feel when it is eaten instead of smoked. So some people eat too much, which can lead to poisoning and/or serious injury.[48-50]

It is also important to remember that marijuana affects children differently than adults. Since marijuana has become legal in some states, children have accidentally eaten marijuana products that looked like candy and treats, which made them sick enough to need emergency care.[43-45, 51]

If you use marijuana products, keep them in childproof containers and out of the reach of children. For additional questions, you can contact your health care provider, the Poison Helpline at 1-800-222-1222, or your health department.

Risk of Using Other Drugs

The concept of marijuana as a “gateway drug”—where using marijuana leads a person to use other drugs—generates a lot of controversy. Researchers haven’t found a definite answer yet.[52, 53]

It is important to remember that people of any age, sex, or economic status can become addicted to marijuana or other drugs. Things can affect the likelihood of substance use include:

  • Family history.
  • Having another mental health illness (such as anxiety or depression).
  • Peer pressure.
  • Loneliness or social isolation.
  • Lack of family involvement.
  • Drug availability.
  • Socioeconomic status.[52, 53]
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