Photo by NIDA
What is marijuana?
Marijuana is the dried leaves and flowers of the Cannabis sativa or Cannabis indica plant. Stronger forms of the drug include high potency strains - known as sinsemilla (sin-seh-me-yah), hashish (hash for short), and extracts.
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 distorts how the mind perceives the world. In other words, it's what makes a person 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 less than 4 percent. It is now about 15 percent and much higher in some products such as oils and other extracts (see below). Scientists do not yet know what this increase in potency means for a person’s health. Some people adjust how they consume marijuana (by smoking or eating less) to compensate for the greater potency. There have been reports of people seeking help in emergency rooms with symptoms, including nervousness, shaking and psychosis (having false thoughts or seeing or hearing things that aren't there), after consuming high concentrations of THC.
Smoking extracts and resins from the marijuana plant with high levels of THC is on the rise. There are several forms of these extracts. These resins have 3 to 5 times more THC than the plant itself. Smoking or vaping it (also called dabbing) can deliver dangerous amounts of THC and has led some people to seek treatment in the emergency room. There have also been reports of people injured in fires and explosions caused by attempts to extract hash oil from marijuana leaves using butane (lighter fluid).
How is marijuana used?
There are a few different ways people use marijuana:
- smoking hand-rolled cigarettes called joints or marijuana cigars called blunts (often made by slicing open cigars and replacing some or all of the tobacco with marijuana)
- inhaling smoke using glass pipes or water pipes called bongs
- inhaling vapor using devices that pull the active ingredients (including THC) from the marijuana into the vapor. Some vaporizers use a marijuana liquid extract.
- drinking tea brewed with marijuana or eating food with marijuana cooked into it, sometimes called edibles—such as brownies, cookies, or candy.
These extracts made from the marijuana plant should not be confused with “synthetic marijuana,” sometimes called “K2,” “Spice,” or “herbal incense.” These synthetic drugs are laboratory-made chemicals similar to THC that are sprayed onto plant materials to make it look like marijuana, but are often much stronger and very dangerous. Unlike marijuana, their use sometimes directly results in overdose deaths. Learn more about "synthetic marijuana”.
What happens to your brain when you use marijuana?
All drugs change the way the brain works by changing the way nerve cells communicate. Nerve cells, called neurons, send messages to each other by releasing chemicals called neurotransmitters. These neurotransmitters attach to molecules on neurons called receptors. (Learn more about how neurotransmitters work.) Drugs affect this signaling process.
When marijuana is smoked or vaporized, THC quickly passes from the lungs into the bloodstream, which carries it to organs throughout the body, including the brain. Its effects begin almost immediately and can last from 1 to 3 hours. This can affect decision making, concentration, and memory for days after use, especially in people who use marijuana regularly.1 If marijuana is consumed in foods or beverages, the effects of THC appear later—usually in 30 minutes to 1 hour—and may last for many hours. Some people consume more and more waiting for the “high” and end up in the emergency room with uncomfortable symptoms from too much THC.
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 activates the endocannabinoid system, which causes the "high" and stimulates the release of dopamine in the brain's reward centers, reinforcing the behavior. Other effects include changes in perceptions and mood, lack of coordination, difficulty with thinking and problem solving, and disrupted learning and memory.
Learn more about how the brain works and what happens when a person uses drugs.
1 Crean 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.
What happens to your body when you use marijuana?
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.
Short term effects include:
- altered senses (such as seeing brighter colors)
- altered sense of time
- changes in mood
- slow reaction time
- problems with balance and coordination
- increased appetite
- trouble thinking and solving problems
- memory problems
- hallucinations (seeing things that aren’t really there)
- delusions (believing something that is not true)
- psychosis (having false thoughts) (risk is highest with regular use of high potency marijuana)
Mixing marijuana with alcohol can cause increased heart rate and blood pressure. It can also cause further slowing of the ability to think, solve problems, and react.
- Increased heart rate. When someone uses marijuana, the heart rate (normally 70 to 80 beats per minute)—may increase or even double, especially if other drugs are taken with the marijuana. This increases the risk of a heart attack.
- Respiratory (lung and breathing) problems. Smoke from marijuana irritates the lungs, and can cause a chronic cough—effects similar to those from regular cigarettes. 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.
- Increased risk for mental health problems. Marijuana use has been linked with depression and anxiety, as well as suicidal thoughts among teens. In addition, research suggests that smoking marijuana during the teen years might increase the risk for developing psychosis in people with a genetic risk for developing schizophrenia. Researchers are still studying the relationship between these mental health problems and marijuana use.
- Increased risk of problems for an unborn baby. Marijuana use during pregnancy is linked to lower birth weight and increased risk of behavioral problems in babies.2
2 The National Academies of Sciences, Engineering, and Medicine, Health and Medicine Division, Board on Population Health and Public Health Practice, Committee on the Health Effects of Marijuana: An Evidence Review and Research Agenda. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington, DC, January 12, 2017. Available at http://nationalacademies.org/hmd/Reports/2017/health-effects-of-cannabis-and-cannabinoids.aspx.
Can you die if you use marijuana?
There are generally no reports of people fatally overdosing (dying) on marijuana alone. However, people can feel some very uncomfortable side effects, especially when using marijuana with high THC levels. There are reports of people who use marijuana seeking treatment in emergency rooms, reporting unease and shaking, anxiety, paranoia, or hallucinations, and in rare cases, extreme psychotic reactions. Learn more about drug overdoses among youth. However, marijuana use can increase risks for accidents and injuries (impacts of drugged driving are discussed below).
What are the other risks associated with marijuana use?
- 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.
- Reduced life satisfaction. Research suggests that 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. 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 using marijuana. Marijuana makes it hard to judge distances and react to signals and sounds on the road. 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 other teens.3 In 2017, 10.3% of 12th graders reported driving after using marijuana in the past two weeks.4 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.
- Use of other drugs. Most young people who use marijuana do not go on to use other drugs. However, those who use are more likely to use other illegal drugs. It isn’t clear why some people go on to try other drugs, but researchers have a few theories. The human brain continues to develop into the early 20s. Exposure to addictive substances, including marijuana, may cause changes to the developing brain that make other drugs more appealing. In addition, someone who uses marijuana is more likely to be in contact with people who use and sell other drugs, increasing the risk for being encouraged or tempted to try them.
- Severe nausea and vomiting. Studies have shown that in rare cases, regular, long-term marijuana use can lead some people to have cycles of severe nausea, vomiting, and dehydration, sometimes requiring visits to the emergency room.
For more information on the effects of marijuana, see NIDA’s Marijuana Research Report.
3 U.S. Department of Transportation. National Highway Traffic Safety Administration. Traffic Safety Facts. Drug Involvement of Fatally Injured Drivers. Washington, DC, November 2010. Available at: http://www-nrd.nhtsa.dot.gov/Pubs/811415.pdf.
4 Miech RA, Schulenberg JE, Johnston LD, et al. National adolescent drug trends in 2017: Findings released [Press release]. Ann Arbor, MI. December 2017. Available at: http://www.monitoringthefuture.org/.
Is marijuana addictive?
Yes, marijuana can be addictive---meaning they continue to use it despite negative consequences.
Approximately 10 percent of people who use marijuana may develop what is called a marijuana use disorder—problems with their health, school, friendships, family or other conflicts in their life. A serious substance use disorder is commonly called an addiction. The person can’t stop using marijuana even though it gets in the way of daily life.5 People who begin using marijuana before the age of 18 are 4–7 times more likely than adults to develop a marijuana use disorder.6
What causes one person to become addicted to marijuana while another does not depends on many factors—including their family history (genetics), the age they start using, if they also use other drugs, their family and friend relationships, and if they take part in positive activities like school, after school clubs or or sports. More research needs to be done to determine if people who use marijuana for medical reasons are at the same risk for addiction as those who use it just to get high.
Watch the Swiss Cheese Model of Drug Addiction and learn why some people who use drugs become addicted and others do not.
People who use marijuana may feel a mild withdrawal when they stop using the drug, but might not recognize their symptoms as drug withdrawal. These 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 may crave the drug to relieve these symptoms.
5 Hasin DS, Saha TD, Kerridge BT, et al. Prevalence of Marijuana Use Disorders in the United States Between 2001-2002 and 2012-2013. JAMA Psychiatry. 2015;72(12):1235-1242. doi:10.1001/jamapsychiatry.2015.1858.
6 Winters KC, Lee C-YS. Likelihood of developing an alcohol and cannabis use disorder during youth: association with recent use and age. Drug Alcohol Depend. 2008;92(1-3):239-247. doi:10.1016/j.drugalcdep.2007.08.005.
How many teens use marijuana?
The chart below shows the percentage of teens who say they use marijuana.
Swipe left or right to scroll.
|Drug||Time Period||8th Graders||10th Graders||12th Graders|
* Data in brackets indicate statistically significant change from the previous year. Previous MTF Data
Explore teen substance use trends over time, by grade and substance with an interactive chart featuring Monitoring the Future data from 2016 to present.
For more statistics on teen drug use, see NIDA’s Monitoring the Future study.
What about medical marijuana?
The marijuana plant itself has not been approved as a medicine by the federal government. However, the plant contains chemicals—called cannabinoids—that may be useful for treating a range of illnesses or symptoms. Here are some samples of cannabinoids that have been approved or are being tested as medicines:
- THC: The cannabinoid that can make you “high”—THC—has some medicinal properties. Two laboratory-made versions of THC, nabilone and dronabinol, have been approved by the federal government to treat nausea, prevent sickness and vomiting from chemotherapy in cancer patients, and increase appetite in some patients with AIDS.
- CBD: Another chemical in marijuana with potential therapeutic effects is called cannabidiol, or CBD. CBD doesn’t have mind-altering effects and is being studied for its possible uses as medicine. For example, CBD oil has been approved as a possible treatment for seizures in children with some severe forms of epilepsy.
- THC and CBD: A medication with a combination of THC and CBD is available in several countries outside the United States as a mouth spray for treating pain or the symptoms of multiple sclerosis.
It is important to remember that smoking marijuana can have side effects, making it difficult to develop as a medicine. For example, it can harm lung health, impair judgment, and affect memory. Side effects like this might outweigh its value as a medical treatment, especially for people who are not very sick. Another problem with smoking or eating marijuana plant material is that the ingredients can vary a lot from plant to plant, so it is difficult to get an exact dose. Until a medicine can be proven safe and effective, it will not be approved by the federal government. But researchers continue to extract and test the chemicals in marijuana to create safe medicines.
For more information, see Drug Facts—Marijuana As Medicine
A growing number of states have legalized the marijuana plant’s use for certain medical conditions, and a smaller number have voted to legalize it for recreational use. So, in some cases, federal and state marijuana laws conflict. 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 misuse. It is important to note that because of concerns over the possible harm to the developing teen brain, non-medical marijuana use by people under age 21 is against the law in all states.
For more information, see Drug Facts—Is Marijuana Medicine?
What should I do if someone I know needs help?
If you, or a friend, are in crisis and need to speak with someone now:
- Call the National Suicide Prevention Lifeline at 1-800-273-TALK (they don't just talk about suicide—they cover a lot of issues and will help put you in touch with someone close by)
If you want to help a friend, you can:
- Share resources from this site, including this page.
- Point your friend to NIDA's Step by Step Guide for Teens and Young Adults.
- Encourage your friend to speak with a trusted adult.
If a friend is using drugs, you might have to step away from the friendship for a while. It is important to protect your own mental health and not put yourself in situations where drugs are being used.
For more information on how to help a friend or loved one, visit our Have a Drug Problem, Need Help? page.
Where can I get more information?
- Commonly Used Drugs Chart
- DrugFacts: Marijuana
- Marijuana: Facts for Teens
- Marijuana: Facts Parents Need to Know
- Mind Matters: The Brain's Response to Marijuana
- Pick Your Poison. Intoxicating Pleasures & Medical Prescriptions: Marijuana [National Library of Medicine]
- The Doctor Is In: Answering Your Marijuana Questions [U.S. Department of Health and Human Services]
Statistics and Trends
- Monitoring the Future
- National Survey on Drug Use and Health [Substance Abuse and Mental Health Services Administration]
- United States Adolescent Substance Abuse Facts (National and State Data) [Office of Adolescent Health]
- Youth Risk Behavior Surveillance System [Centers for Disease Control and Prevention]