What Is Marijuana?
Also known as: “weed,” “pot,” “bud,” “grass,” “herb,” “Mary Jane,” “MJ,” “reefer,” “skunk,” “boom,” “gangster,” “kif,” “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 hash oil.
Of the approximately 400 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 how the brain works, distorting how the mind perceives the world.
It is illegal to 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, marijuana state laws for adult use are changing. As of 2014, more than 20 states have passed laws allowing the use of marijuana as a treatment for certain medical conditions.
In addition, two states have legalized marijuana for adult recreational use. Because of concerns over the possible harm to the developing teen brain and the risk of driving under the influence, marijuana use by people under age 21 is prohibited in all states.
Strength and Potency
The amount of THC in marijuana has increased over the past few decades—from 4% in the 1980s to almost 15% in 2012.1 Scientists don’t yet know what this increase in potency means for a person’s health. It could be that users take in higher amounts of THC, or they may adjust how they consume marijuana (like smoke or eat less) to compensate for the greater potency.
The honey-like resin from the marijuana plant has 3 to 5 times more THC than the plant itself. Smoking it (also called “dabbing”) can lead to dangerous levels of intoxication requiring emergency treatment. People have been burned in fires and explosions caused by attempts to extract hash oil using butane (lighter fluid).
How Is Marijuana Used?
The most common method is smoking loose marijuana rolled into a cigarette called a “joint” or “nail.” Sometimes marijuana is smoked through a water pipe called a “bong.” It can also be combined with tobacco and filled into hollowed out cigars, known as “blunts,” and smoked. Marijuana can also be brewed as tea or mixed with food, sometimes called edibles.
How Does Marijuana Affect the Brain?
The main chemical in marijuana that affects the brain is delta-9-tetrahydrocannabinol (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 cells are activated by chemicals 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 endocannabinoid system. One of the effects is a release of dopamine in the brain, which creates 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:
Marijuana’s Effects on the Brain
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 and continued into adulthood had a large drop in IQ, even if they quit.
Coordination. THC affects the cerebellum, the section of our brain that controls balance and coordination, and the basal ganglia, another part of the brain that helps control movement. These effects can affect performance in such activities as sports, driving, and video games.
Judgment. Since marijuana can affect 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, its effects begin almost immediately and can last from 1 to 3 hours. Decision-making, concentration, and memory can suffer for days after use, especially in regular users.2
If marijuana is consumed in foods or beverages, the effects of THC appear later—usually in 30 minutes to 1 hour—but can last up to 4 hours.
Long-term, regular use of marijuana—starting in the teen years—may impair brain development and lower IQ, meaning the brain may not reach its full potential.3,4
What Are the Other Effects of Marijuana?
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. Although we don’t yet know if marijuana causes lung cancer, many people who smoke marijuana also smoke cigarettes, which do cause cancer. And, smoking marijuana can make it harder to quit cigarette smoking.
Increased risk for mental health problems. Marijuana use has been linked with depression and anxiety, suicidal thoughts among adolescents, and increased risk for people with a family history of developing schizophrenia, and developing it 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 may contribute to problems with attention, memory, and problem solving. Pregnant women who use marijuana also may smoke cigarettes or drink alcohol, both of which can affect the baby’s development.
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 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 a number of 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. Marijuana is the most common illegal drug involved in auto fatalities. High school seniors who smoke marijuana are 2 times more likely to receive a traffic ticket and 65% more likely to get into an accident than those who don’t smoke.5 In 2011, among 12th graders, 12.5% reported that within the past 2 weeks they had driven after using marijuana.6 And combining marijuana with drinking even a small amount of alcohol greatly increases driving danger, more than either drug alone. Learn more about what happens when you mix marijuana and driving.
Potential gateway to other drugs. Studies of drug use patterns show that of high school students who use other illegal drugs, most of them had first tried marijuana. However, many young people who use marijuana do not go on to use other drugs. It isn’t clear why some people do go on to try other drugs, but researchers have a few theories. Exposure to marijuana may affect the brain, particularly during development, which continues into the early 20s. Effects may include changes to the brain that make other drugs more appealing. Animal research supports this possibility—for example, early exposure to marijuana makes opiate drugs (like Vicodin or heroin) more pleasurable. In addition, someone who uses marijuana is likely to be in contact with people who use and sell other drugs, increasing the risk for being encouraged or tempted to try them. Finally, people at high risk for using drugs may use marijuana first because it is easy to get (like cigarettes and alcohol).
Can You Get Addicted to Marijuana?
Yes, marijuana is 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.
It is estimated that about 1 in 6 people who start using as a teen, and 25% to 50% percent of those who use it every day, become addicted to marijuana. What causes one person to become addicted to marijuana and another not to depends on many factors—including your family history (genetics), the age you start using, whether you also use other drugs, your family and friend relationships, and success in school (environment).
People who use marijuana may also feel withdrawal when they stop using the drug. Withdrawal symptoms may include:
- Lack of appetite, which can lead to weight loss
- Drug cravings
These effects can last for several days to a few weeks after drug use is stopped. Relapse (returning to the drug after you’ve quit) is common during this period because people also crave the drug to relieve these symptoms.
Can You Die If You Use Marijuana?
It is very unlikely for a person to overdose and die from marijuana use. However, people can and do injure themselves and die because of marijuana’s effects on judgment, perception, and coordination, for example, when driving under the influence of the drug. In fact, marijuana was a factor in over 370,000 visits to the emergency department in 2009. About two-thirds of those patients were male, and 12% were teens ages 12 to 17.7
Additionally, people can experience extreme anxiety (panic attacks) or psychotic reactions (where they lose touch with reality and may become paranoid).
Is Marijuana Addictive?
Contrary to common belief, marijuana is addictive. Estimates from research suggest that about 9 percent of users become addicted to marijuana; this number increases among those who start young (to about 17 percent, or 1 in 6) and among people who use marijuana daily (to 25-50 percent).
Long-term marijuana users trying to quit report withdrawal symptoms including irritability, sleeplessness, decreased appetite, anxiety, and drug craving, all of which can make it difficult to abstain. Behavioral interventions, including cognitive-behavioral therapy and motivational incentives (i.e., providing vouchers for goods or services to patients who remain abstinent) have proven to be effective in treating marijuana addiction. Although no medications are currently available, recent discoveries about the workings of the endocannabinoid system offer promise for the development of medications to ease withdrawal, block the intoxicating effects of marijuana, and prevent relapse.
How Does Marijuana Affect a User’s Life?
Research shows marijuana may cause problems in daily life or make a person’s existing problems worse. Heavy marijuana users generally report lower life satisfaction, poorer mental and physical health, more relationship problems, and less academic and career success compared to non-marijuana-using peers. For example, marijuana use is associated with a higher likelihood of dropping out of school. Several studies also associate workers’ marijuana smoking with increased absences, tardiness, accidents, workers’ compensation claims, and job turnover.
1Volkow ND, Crane NA, Mason BJ. Adverse health effects of marijuana use. New England Journal of Medicine. 2014 Jun 5;370(23):2219-27. doi: 10.1056/NEJMra1402309.
2Crean RD, Crane NA, Mason BJ. An evidence based review of acute and long-term effects of cannabis use on executive cognitive functions. Journal of Addiction Medicine 2011;5:1-8.
3Zalesky A, Solowij N, Yücel M, et al. Effect of long-term cannabis use on axonal fibre connectivity. Brain 2012;135:2245-55.
4Meier MH, Caspi A, Ambler A, et al. Persistent cannabis users show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Sciences U S A 2012;109:E2657-64.
5U.S. Department of Transportation. National Highway Traffic Safety Administration. Traffic Safety Facts. Drug Involvement of Fatally Injured Drivers. Washington, DC, November 2010.
6O’Malley, P.M.; Johnston, L.D. Driving after drug or alcohol use by U.S. high school seniors, 2001–2011. American Journal of Public Health 103(11):2027-2034, 2013.
7Substance Abuse and Mental Health Services Administration. Office of Applied Studies. Drug Abuse Warning Network, 2009: National Estimates of Drug-Related Emergency Department Visits. DHHS Publication No. (SMA) 11-4659, DAWN Series D-35. Rockville, MD, 2011.