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. 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 week may be taking in as many cancer-causing chemicals as someone who smokes a full pack of cigarettes every day. 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. People with HIV and others whose immune system is impaired should avoid marijuana use. People who smoke marijuana often develop the same kinds of breathing problems that cigarette smokers have. They have symptoms of daily cough and phlegm (chronic bronchitis) and more frequent chest colds. They are also at greater risk of getting lung infections such as pneumonia. Continued marijuana smoking can lead to abnormal function of the lungs and airways. Scientists have found signs of lung tissue injured or destroyed by marijuana smoke.
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.
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.
