By Erin Allday /SFGate / January 10, 2012
Smoking a joint or a bowl from time to time appears to cause no long-term damage to the lungs, according to a UCSF study that disproves one of the major concerns about marijuana use – that inhaling anything other than air on a regular basis must be harmful.
The study, results of which were published today in the Journal of the American Medical Association, found that the lung capacity of people who smoked marijuana was not diminished by lighting up, even among those who smoked once or twice a week.
Smoking 20 or more joints a month did have a negative impact on the pulmonary system, but that level of marijuana use is unusual. For occasional users, smoking marijuana was actually associated with a small but statistically significant increase in lung capacity – perhaps caused by the deep-breathing pot smokers use to draw the drug into their lungs.
Researchers were reluctant to give the all clear to anyone who wants to smoke pot, but the results – and the fact that they were published in a major medical journal – should reassure doctors and patients who are tempted to use marijuana for treatment, primarily to ease pain and nausea, said Dr. Mark Pletcher, a UCSF epidemiologist and lead author of the study.
“Moderate levels of exposure to marijuana don’t seem to have any adverse effects in terms of pulmonary function,” Pletcher said. “That was a little surprising to me, honestly. I thought we were going to find a small decline in pulmonary function, similar to what we’d find with tobacco.”
Smoking cigarettes has such dramatic, long-term health consequences – including emphysema and lung cancer – that doctors have long assumed that marijuana smoking, too, must be detrimental.
The study, which looked at 5,115 men and women over a 20-year period, found that people were just about as likely to smoke marijuana as cigarettes, and many participants smoked both. People who smoked cigarettes, however, were more likely to be heavy users – on average about eight cigarettes a day – than marijuana smokers, who lit up on average two or three times a month.
It’s likely that the main reason that marijuana smoke doesn’t seem to affect lung function the way tobacco does is because people simply don’t use the drug as much as they use tobacco. But it’s also possible, scientists said, that marijuana smoke just isn’t as damaging as tobacco smoke.
“No one would ever claim that drinking water has the same effect as drinking vodka, even though they’re both liquids and you’re ingesting them the same way. But for some reason we have assumed that because we know the negative outcomes with cigarettes, inhaling any plant material is going to have the same outcomes,” said Amanda Reiman, a UC Berkeley lecturer and director of research at the Berkeley Patients Group, a medical marijuana dispensary.
“This study is challenging the preconceived notions we’ve had for some time about the dangers of smoking cannabis and the similarities to smoking tobacco,” she said.