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).
For more information on the effects of marijuana, see our Marijuana Research Report.
5. 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.