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Other Names: Hash, Pot, Weed

Also known as: Weed, Pot, Bud, Grass, Herb, Mary Jane, MJ, Reefer, Skunk, Boom, Gangster, Kief, Chronic, and Ganja

Marijuana is a mixture of the dried and shredded leaves, stems, seeds, and flowers of Cannabis sativa—the hemp plant. The mixture can be green, brown, or gray. Stronger forms of the drug include sinsemilla (sin-seh-me-yah), hashish (hash for short), and extracts including hash oil, shatter, wax, and budder.

Of the more than 500 chemicals in marijuana, delta-9-tetrahydrocannabinol, known as THC, is responsible for many of the drug’s psychotropic (mind-altering) effects. It’s this chemical that changes brain activity, distorting how the mind perceives the world.

Legal Issues

Currently, Federal and state marijuana laws conflict with each other. It is illegal to grow, buy, sell, or carry marijuana under Federal law. The Federal Government considers marijuana a Schedule I substance—having no medicinal uses and high risk for abuse. However, across the United States, state marijuana laws for adult use are changing. A growing number of states have passed laws allowing the use of marijuana as a treatment for certain medical conditions.

In addition, several states and the District of Columbia have legalized marijuana for adult recreational use. Because of concerns over the possible harm to the developing teen brain, marijuana use by people under age 21 is prohibited in all states (although some states allow children with severe epilepsy to use cannabidiol, a chemical found in marijuana that does not produce a “high”).

Strength and Potency

The amount of THC in marijuana has increased over the past few decades. In the early 1990s, the average THC content in marijuana was about 3.74 percent. In 2013, it was almost 10 percent, and much higher in some products such as oils and other extracts (see below).1 Scientists do not yet know what this increase in potency means for a person’s health. It may cause users to take in higher amounts of THC – which could lead to greater health risks including increased risk of addiction, or they may adjust how they consume marijuana (by smoking or eating less) to compensate for the greater potency.

Marijuana Extracts

Smoking resins of THC from the marijuana plant is on the rise. There are several forms of the extracts, such as hash oil or honey oil, wax, and shatter. These resins have 3 to 5 times more THC than the plant itself. Smoking it (also called dabbing) can deliver dangerous amounts of THC to users, and has led some people to the emergency room. People have, also, been burned in fires and explosions caused by attempts to extract hash oil from marijuana leaves using butane (lighter fluid).

The main chemical in marijuana that affects the brain is THC. When marijuana is smoked, THC quickly passes from the lungs into the bloodstream, which carries it to organs throughout the body, including the brain. As it enters the brain, THC attaches to cells, or neurons, with specific kinds of receptors called cannabinoid receptors. Normally, these receptors are activated by chemicals similar to THC that occur naturally in the body. They are part of a communication network in the brain called the endocannabinoid system. This system is important in normal brain development and function.

Most of the cannabinoid receptors are found in parts of the brain that influence pleasure, memory, thinking, concentration, sensory and time perception, and coordinated movement. Marijuana triggers an increase in the activity of the endocannabinoid system, which causes the release of dopamine in the brain's reward centers, creating the pleasurable feelings or “high.” Other effects include changes in perceptions and mood, lack of coordination, difficulty with thinking and problem solving, and disrupted learning and memory.

Certain parts of the brain have a lot of cannabinoid receptors. These areas are the hippocampus, the cerebellum, the basal ganglia, and the cerebral cortex. (Learn more about these areas and how THC affects them.) The functions that these brain areas control are the ones most affected by marijuana:

  • Learning and memory. The hippocampus plays a critical role in certain types of learning. Disrupting its normal functioning can lead to problems studying, learning new things, and recalling recent events. A recent study followed people from age 13 to 38 and found that those who used marijuana a lot in their teens had up to an 8-point drop in IQ, even if they quit in adulthood.
  • Coordination. THC affects the cerebellum, the area of our brain that controls balance and coordination, and the basal ganglia, another part of the brain that helps control movement. These effects can influence performance in such activities as sports, driving, and video games.
  • Judgment. Since THC affects areas of the frontal cortex involved in decision making, using it can cause you to do things you might not do when you are not under the influence of drugs—such as engaging in risky sexual behavior, which can lead to sexually transmitted diseases (STDs) like HIV, the virus that causes AIDS—or getting in a car with someone who’s been drinking or is high on marijuana.

When marijuana is smoked, or vaporized, its effects begin almost immediately and can last from 1 to 3 hours. If marijuana is consumed in foods or beverages, the effects of THC appear later—usually in 30 minutes to 1 hour—but may last for many hours.

The changes that take place in the brain when a person uses marijuana can cause serious health problems and affect a person’s daily life.

Effects on Health

Within a few minutes after inhaling marijuana smoke, a person’s heart rate speeds up, the bronchial passages (the pipes that let air in and out of your lungs) relax and become enlarged, and blood vessels in the eyes expand, making the eyes look red. While these and other effects seem harmless, they can take a toll on the body.

  • Increased heart rate. When someone uses marijuana, heart rate—normally 70 to 80 beats per minute—may increase by 20 to 50 beats per minute or, in some cases, even double. This effect can be greater if other drugs are taken with marijuana. The increased heart rate forces the heart to work extra hard to keep up.
  • Respiratory (lung and breathing) problems. Smoke from marijuana irritates the lungs, causing breathing and lung problems among regular users similar to those experienced by people who smoke tobacco—like a daily cough and a greater risk for lung infections such as pneumonia. While research has not found a strong association between marijuana and lung cancer, many people who smoke marijuana also smoke cigarettes, which do cause cancer. And, some studies have suggested that smoking marijuana could make it harder to quit cigarette smoking.
  • Increased risk for mental health problems. Marijuana use has been linked with depression and anxiety, as well as suicidal thoughts among adolescents. In addition, research has suggested that in people with a genetic risk for developing schizophrenia, smoking marijuana during adolescence may increase the risk for developing psychosis and for it developing at an earlier age. Researchers are still learning exactly what the relationship is between these mental health problems and marijuana use.
  • Increased risk of problems for an unborn baby. Pregnant women who use marijuana may risk changing the developing brain of the unborn baby. These changes could contribute to problems with attention, memory, and problem solving. Studies also show that marijuana use during pregnancy leads to low birth weight, and a higher risk of stillbirth.
Effects on School and Social Life

The effects of marijuana on the brain and body can have a serious impact on a person’s life.

  • Reduced school performance. Students who smoke marijuana tend to get lower grades and are more likely to drop out of high school than their peers who do not use. The effects of marijuana on attention, memory, and learning can last for days or weeks. These effects have a negative impact on learning and motivation. In fact, people who use marijuana regularly for a long time are less satisfied with their lives and have more problems with friends and family compared to people who do not use marijuana.
  • Impaired driving. It is unsafe to drive while under the influence of marijuana. Marijuana affects many skills required for safe driving—alertness, concentration, coordination, and reaction time—so it’s not safe to drive high or to ride with someone who’s been smoking. Marijuana makes it hard to judge distances and react to signals and sounds on the road.

Yes, marijuana can be addictive. A user may feel the urge to smoke marijuana again and again to re-create the “high.” Repeated use could lead to addiction—which means the person has trouble controlling their drug use and often cannot stop even though they want to.

An estimated 30 percent of users may develop some degree of problem use—use that causes problems with a person’s health, school, or other aspects of life, also known as a marijuana use disorder. Such a disorder is called an addiction when the person can’t stop using marijuana even though it gets in the way of daily life. People who begin using marijuana before the age of 18 are 4–7 times more likely than adults to develop a marijuana use disorder.

Chemistry. Marijuana’s main psychoactive chemical is delta-9-tetrahydro-cannabinol, commonly known as THC. Due to the variety of strains, potency, and the effects it can produce, marijuana can be categorized as a depressant, a hallucinogen, or a stimulant, making it difficult to predict how individuals may react.

Here are the generally accepted short-term physiological effects of each drug class:

  • Depressants make individuals feel tired, slow, relaxed, unfocused, uncoordinated and unable to think clearly.
  • Hallucinogens may cause abnormal visual or auditory experiences, unusual thoughts, or altered awareness.
  • Stimulants can lead to anxiety, agitation, and increased heart rate.

The answer to this question depends on many factors—including their family history (genetics), the age they start using, whether they also use other drugs, their family and friend relationships, and whether they take part in positive activities like school or sports. (environment). More research needs to be done to determine whether people who use marijuana for medical reasons are at the same risk as those who use it recreationally.

Yes, we've created a visual to help convey important information for parents looking for facts and tips on how to talk with their children about marijuana.

Click here to print/view our latest infographic:  "Marijuana Use and Parenting: What You Need to Know"

Learn About THC Concentrates
  • a gooey liquid wax (hash oil or honey oil)
  • a soft solid with a texture like lip balm (wax or budder)
  • a hard, amber-colored solid (shatter)

Oil and waxes can be consumed using vape pens. Solids can also be placed on a heated platform where they are vaporized by high heat and inhaled through a dabbing tool, often called a rig.


The number of seniors who reported vaping marijuana during the past month increased from 7.5% in 2018 to 14% in 2019. This is the second largest one-year jump for any substance in the 45-year survey history, behind past month nicotine vaping (2017 to 2018).

Source: National Institute on Drug Abuse; National Institutes of Health; U.S. Department of Health and Human Services.
Tips for Teens: The Truth About Marijuana

Substance Abuse and Mental Health Services Administration (SAMHSA)

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