Q: What are the long-term effects of marijuana use?
A: Findings so far show that regular use of marijuana or THC may play a role in some kinds of cancer and in problems with the respiratory and immune systems.
- Cancer
It’s hard to know for sure whether regular marijuana use causes cancer. But it is known that marijuana contains some of the same, and sometimes even more, of the cancer-causing chemicals found in tobacco smoke. 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 (15)
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- Lungs and airways
People who smoke marijuana often develop the same kinds of breathing problems that cigarette smokers have: coughing and wheezing. They tend to have more chest colds than nonusers. They are also at greater risk of getting lung infections like pneumonia.
- Immune system
Animal studies have found that THC can damage the cells and tissues in the body that help protect against disease. When the immune cells are weakened you are more likely to get sick.
Q: Does marijuana lead to the use of other drugs?
A: It could. Long-term studies of high school students and their patterns of drug use show that very few young people use other illegal drugs without first trying marijuana (7). 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 are users and sellers of other drugs. So there is more of a risk that a marijuana user will be exposed to and urged to try more drugs.
To better determine this risk, scientists are examining the possibility that long-term marijuana use may create changes in the brain that make a person more at risk of becoming addicted to other drugs, such as alcohol or cocaine. Further research is needed to predict who will be at greatest risk.
Q: How can you tell if someone has been using marijuana?
A: If someone is high on marijuana, he or she might
- seem dizzy and have trouble walking;
- seem silly and giggly for no reason;
- have very red, bloodshot eyes; and
- have a hard time remembering things that just happened.
When the early effects fade, over a few hours, the user can become very sleepy.
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