It is true that long-term chronic pot smoking can contribute to lung damage:
However, certain cellular abnormalities in the lungs have been identified more frequently in long-term smokers of cannabis compared to non-smokers. Chronic exposure to cannabis smoke has also been associated with the development of pre-cancerous changes in bronchial and epithelium cells in similar rates to tobacco smokers. Cellular abnormalities were most present in individuals who smoked both tobacco and marijuana, implying that cannabis and tobacco smoke may have an additive adverse effect on airway tissue. The results suggest that long-term exposure to cannabis smoke, particularly when combined with tobacco smoking, is capable of damaging the bronchial system in ways that could one day lead to respiratory cancers. However, to date, no epidemiologic studies of cannabis-only smokers have yet to reveal such a finding. Larger, better-controlled studies are warranted.
However,
Moderate Marijuana Use Does Not Impair Lung Function, Study Finds
The researchers followed more than 5,000 people over two decades and found that regularly smoking marijuana — the equivalent of up to a joint a day over seven years — did not impair performance on a lung function test. The test, a measure of pulmonary obstruction that looks at the amount of air a person can force out in one second after taking a deep breath, is typically worsened by smoking tobacco.
While tobacco smokers showed the expected drop in lung function over time, the new research found that marijuana smoke had unexpected and apparently positive effects. Low to moderate users actually showed increased lung capacity compared to nonsmokers on two tests, known as FEV1 and FVC. FEV1 is the amount of air someone breathes out in the first second after taking the deepest possible breath; FVC is the total volume of air exhaled after the deepest inhalation.
So while there is evidence that smoking pot doesn't affect lung
function:
“FEV1 and FVC both actually increased with moderate and occasional use of marijuana,” says Dr. Mark Pletcher, associate professor of epidemiology and biostatistics at the University of California, San Francisco and the lead author of the study.
That was a bit of a surprise, says Pletcher, since “There are clearly adverse effects from tobacco use and marijuana smoke has a lot of the same constituents as tobacco smoke does so we thought it might have some of the same harmful effects. It’s a weird effect to see and we couldn’t make it go away,” he adds, explaining that the researchers used statistical models to look for errors or other factors that could explain the apparent benefit and did not find them.
The improvement wasn’t seen in the heaviest users, however. At high levels of marijuana use—for example, in those who smoked more than 20 times a month—FEV1 slipped back to levels seen in nonusers and a reduction was seen in, um, the most chronic smokers. But FVC remained high in even the longest term, heaviest users.
In something of a twist, the researchers found that compared to nonsmokers, marijuana users performed slightly better on the lung function test, though the improvement was minuscule. “Even with this tiny increase in airflow, I have to admit that I really doubt that there’s any real increase in lung health,” said Dr. Stefan Kertesz, an associate professor at the University of Alabama at Birmingham school of medicine and an author of the study. The finding may merely reflect marijuana smokers’ years of “training” in taking deep inhalations and holding the smoke, the researchers said.
there seems to still be an opinion that long-term heavy smoking can be bad. Personally, I don't see that as an indictment of pot, but rather of sucking on any large quantity of smoke for years on end. Combine that with heavy Cheetos abuse and who knows.
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