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What Are the Long-Term Health Effects of Marijuana Use?

The Brain

When people smoke marijuana for years, they can suffer some pretty negative consequences. For example, because marijuana affects brain function, your ability to do complex tasks could be compromised, as well as your pursuit of academic, athletic, or other life goals that require you to be 100-percent focused and alert. In fact, people who use marijuana over the long term self-report less life satisfaction, poorer education, and job achievement, and more interpersonal and mental health problems compared to people who do not use marijuana.

Marijuana also may affect your mental health. Studies show that early marijuana use may increase your risk of developing psychosis if you have a genetic vulnerability to the disease. Psychosis is a severe mental disorder in which there is a loss of contact with reality, including false ideas about what is happening (delusions) and seeing or hearing things that aren’t there (hallucinations). Marijuana also has been associated with depression and anxiety, but more research is necessary to confirm and better understand that relationship.

Addiction

Many people don’t think of marijuana as addictive—they are wrong. About 9 percent of people who use marijuana become dependent on it. The number increases to about one in six among those who start using it at a young age, and to 25 to 50 percent among daily users. Marijuana increases dopamine, which creates the good feelings or “high” associated with its use. A user may feel the urge to smoke marijuana again, and again, and again to re-create that experience. Repeated use could lead to addiction—a disease where people continue to do something, even when they are aware of the severe negative consequences at the personal, social, academic, and professional levels.

People who use marijuana may also experience a withdrawal syndrome when they stop using the drug. It is similar to what happens to tobacco smokers when they quit—people report being irritable, having sleep problems, and weight loss—effects which can last for several days to a few weeks after drug use is stopped. Relapse is common during this period, as users also crave the drug to relieve these symptoms.

Lungs and Airways

People who abuse marijuana are at risk of injuring their lungs through exposure to respiratory irritants and carcinogens found in marijuana smoke. The smoke from marijuana contains some of the same chemicals found in tobacco smoke; plus, marijuana users tend to inhale more deeply and hold their breath longer, so more smoke enters the lungs. Not surprisingly, people who smoke marijuana have some of the same breathing problems as those who smoke tobacco—they are more susceptible to chest colds, coughs, and bronchitis than people who do not smoke. And, even though we don’t know yet whether or how marijuana use affects the risk for lung and other cancers—why take the risk?

Does Marijuana Use Lead to the Use of Other Drugs?

While most people who smoke marijuana do not go on to use other drugs, long-term studies of high school students show that few young people use other illegal drugs without first trying marijuana. For example, the risk of using cocaine is much greater for those who have tried marijuana than for those who have never tried it. Using marijuana puts children and teens in contact with people who use and sell other drugs. So, a person who uses marijuana is more likely to be exposed to and urged to try other drugs. The effects of marijuana on the brain of adolescents—still a work in progress—may also affect their likelihood of using other drugs as they get older. Animal studies suggest this to be true, but it is not yet demonstrated in people.

What About Medical Marijuana?

Under U.S. law since 1970, marijuana has been a Schedule I controlled substance. This means that the drug has no approved medical use. However, there are medications containing synthetic THC, the main active ingredient in marijuana, that are used to treat nausea in cancer patients undergoing chemotherapy, and to stimulate appetite in patients with wasting syndrome—severe, involuntary weight loss—due to AIDS.

Since the discovery of the cannabinoid system—receptors in the body that bind THC, and chemicals that act as these receptors—scientists are actively looking for ways to use this system for medical purposes. Several promising compounds are being tested for the treatment of obesity, pain, and other disorders. However, it is unlikely that smoked marijuana will be developed as a medication because of its negative health effects.

What If a Person Wants To Quit Using the Drug?

Researchers are testing different ways to help people who use marijuana abstain from drug use. Currently, no medications exist for treating marijuana addiction. Treatment programs focus on behavioral therapies. A number of programs are designed specifically to help teenagers who abuse marijuana.

When someone has a drug problem, it's not always easy to know what to do. If someone you know is using marijuana, encourage him or her to talk to a parent, school guidance counselor, or other trusted adult. There are also anonymous resources, such as the National Suicide Prevention Lifeline (1-800-273-TALK) and the Treatment Referral Helpline (1-800-662-HELP).

The National Suicide Prevention Lifeline (1-800-273-TALK) is a crisis hotline that can help with a lot of issues, not just suicide. For example, anyone who feels sad, hopeless, or suicidal; family and friends who are concerned about a loved one; or anyone interested in mental health treatment referrals can call this Lifeline. Callers are connected with a professional nearby who will talk with them about what they’re feeling or concerns for other family and friends.

In addition, the Treatment Referral Helpline (1-800-662-HELP)—offered by the Substance Abuse and Mental Health Services Administration—refers callers to treatment facilities, support groups, and other local organizations that can provide help for their specific need. You can also locate treatment centers in your state by going to www.findtreatment.samhsa.gov.

Resource Materials

1.	National Institute on Drug Abuse. Marijuana: Facts for Teens (http://www.drugabuse.gov/publications/marijuana-facts-teens). NIH Pub. No. 98-4037. Bethesda, MD. NIDA, NIH, DHHS. Revised March 2011. Retrieved June 2009.
2.	National Institute on Drug Abuse. Marijuana: Facts Parents Need to Know (http://www.drugabuse.gov/publications/marijuana-facts-parents-need-to-know). NIH Pub. No. 02-4036. Bethesda, MD. NIDA, NIH, DHHS. Revised August 2011. Retrieved June 2009.
3.	National Institute on Drug Abuse. Monitoring the Future. National Results on Adolescent Drug Use. Overview of Key Findings 2010. (http://www.monitoringthefuture.org/pubs/monographs/mtf-overview2010.pdf). Bethesda, MD. NIDA, NIH, DHHS. February 2011. Retrieved June 2011.
4.	National Institute on Drug Abuse. NIDA Research Report: Marijuana Abuse (http://www.drugabuse.gov/ResearchReports/Marijuana/ default.html). NIH Pub. No. 00-3859. Bethesda, MD. NIDA, NIH, DHHS. Revised September 2010. Retrieved June 2009.
5.	National Institute on Drug Abuse. Monitoring the Future. Data Tables and Figures (http://monitoringthefuture.org/data/10data/pr10t3.pdf, http://monitoringthefuture.org/data/10data/pr10t2.pdf). Bethesda, MD. NIDA, NIH, DHHS. December 2010. Retrieved June 2011.

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This page was last updated in October 2011.