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Marijuana 101

What is marijuana?

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. 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”). Read more about marijuana-related state laws.

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. 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.

ElSohly MA. Potency Monitoring Program quarterly report number 124. Reporting period: 12/16/2013 -03/15/2014. Bethesda, MD: National Institute on Drug Abuse; 2014.

Effects of marijuana

When marijuana is smoked or vaporized, 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. 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.

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.

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. Read on to learn more.

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.

Meier 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.

Meier 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.

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. Pregnant women who use marijuana also increase the risk of a baby with a lower birth weight.
Panlilio, LV, et al. Prior exposure to THC increases the addictive effects of nicotine in rats. Neuropsychopharmacology (2013) 38, 1198–1208.

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 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.  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. In 2011, among 12th graders, 12.5% reported that within the past 2 weeks they had driven after using marijuana. 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. Most young people who use marijuana do not go on to use other drugs. However, those who use marijuana, alcohol, or tobacco during their teen years 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. Finally, people at high risk for using drugs may use marijuana first because it is easy to get (like cigarettes and alcohol).
U.S. Department of Transportation. National Highway Traffic Safety Administration. Traffic Safety Facts. Drug Involvement of Fatally Injured Drivers. Washington, DC, November 2010. Available here.
O’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.
Get Help Now

If you or someone you know needs to talk to someone right now, text HOME to 741-741 or call 1-800-273-TALK (8255) for a free confidential conversation with a trained counselor 24/7. 

If you are experiencing a mental health crisis, text or call 988.

If this is a medical emergency or if there is immediate danger of harm, call 911 and explain that you need support for a mental health crisis.

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