Long-Term Effects on the Body
Like tobacco smoke, marijuana smoke is an irritant to the throat and lungs and can cause a heavy cough during use. It also contains levels of volatile chemicals and tar that are similar to tobacco smoke, raising concerns about risk for cancer and lung disease.
Marijuana smoking is associated with large airway inflammation, increased airway resistance, and lung hyperinflation, and those who smoke marijuana regularly report more symptoms of chronic bronchitis than those who do not smoke. People who frequently smoke marijuana have more outpatient medical visits for respiratory problems than non-smokers. However, studies have not found that marijuana increases risk for emphysema.
For people with immune deficiencies, smoking marijuana might increase susceptibility to lung infections (such as pneumonia), thanks to THC’s immune-suppressing effects.
THC and CBD may have antitumor effects, which has been proposed as one reason why stronger associations are not seen between marijuana use and lung cancer, but more research is needed on this question.
Lung Health: Marijuana vs. Tobacco
Comparing the lung health risks posed by marijuana and tobacco is complex, as these substances are used differently. While people who smoke marijuana often inhale more deeply and hold the smoke in their lungs for a longer duration than is typical with cigarettes, marijuana’s effects last longer, so marijuana users may smoke less frequently than those who smoke cigarettes.
Additionally, the fact that many people use both marijuana and tobacco makes determining marijuana’s precise contribution to lung cancer risk, if any, difficult to establish.
Within a few minutes after inhaling marijuana smoke, a person’s heart rate speeds up, the breathing passages relax and become enlarged, and blood vessels in the eyes expand, making the eyes look bloodshot. The heart rate—normally 70 to 80 beats per minute—may increase by 20 to 50 beats per minute or may even double in some cases. Taking other drugs with marijuana can amplify this effect.
Some evidence suggests that a person’s risk of heart attack during the first hour after smoking marijuana is nearly five times his or her usual risk. This observation could be partly explained by marijuana raising blood pressure (in some cases) and heart rate, and reducing the blood’s capacity to carry oxygen.
Marijuana may also cause orthostatic hypotension (head rush or dizziness on standing up), possibly raising danger from fainting and falls.
Tolerance to some cardiovascular effects often develops with repeated exposure. These health effects need to be examined more closely, particularly given the increasing use of medical marijuana by people with health issues and older adults who may have increased baseline vulnerability due to age-related cardiovascular risk factors.