What Are the Long-Term Effects of Marijuana?

Long term effects of Pot
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Question: What Are the Long-Term Effects of Marijuana?

Answer: While all of the long-term effects of marijuana use are not yet known, there are studies showing serious health concerns. For example, a group of scientists in California examined the health status of 450 daily smokers of marijuana but not tobacco. They found that the marijuana smokers had more sick days and more doctor visits for respiratory problems and other types of illness than did a similar group who did not smoke either substance.

Findings so far show that the regular use of marijuana or THC may play a role in cancer and problems in the respiratory, and immune systems.


It is hard to find out whether marijuana alone causes cancer because many people who smoke marijuana also smoke cigarettes and use other drugs. Marijuana smoke contains some of the same cancer-causing compounds as tobacco, sometimes in higher concentrations. Studies show that someone who smokes five joints per day may be taking in as many cancer-causing chemicals as someone who smokes a full pack of cigarettes every day.

Tobacco smoke and marijuana smoke may work together to change the tissues lining the respiratory tract. Marijuana smoking could contribute to early development of head and neck cancer in some people. Smoking marijuana has also been linked to testicular cancer.

Immune System

Our immune system protects the body from many agents that cause disease.

It is not certain whether marijuana damages the immune system of people. But both animal and human studies have shown that marijuana impairs the ability of T-cells in the lungs' immune defense system to fight off some infections.

Lungs and Airways

People who smoke marijuana regularly may develop many of the same breathing problems that tobacco smokers have, such as daily cough and phlegm production, more frequent chest colds, a heightened risk of lung infections, and a greater tendency toward obstructed airways.

Cancer of the respiratory tract and lungs may also be promoted by marijuana smoke, since it contains irritants and carcinogens.

Marijuana smokers usually inhale more deeply and hold their breath longer, which increases the lungs' exposure to carcinogenic smoke. Thus, puff for puff, smoking marijuana may increase the risk of cancer more than smoking tobacco does.

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Chuder, Eric C., "Neuroscience for Kids: Marijuana," University of Washington, Revised 2008.

SAMHSA's National Clearinghouse for Alcohol & Drug Information. "Tips for Teens: The Truth About Marijuana," Revised May 2004.

National Institute on Drug Abuse. "Marijuana: Facts Parents Need to Know." Revised August 2007.

Tetrault, J.M., et al. "Effects of marijuana smoking on pulmonary function and respiratory complications: a systematic review." Archives of Intern Medicine. February 2007.

Mehra, R, et al. "The association between marijuana smoking and lung cancer: a systematic review." Archives of Internal Medicine. July 2006.

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