January 10th, 2012
05:11 PM ET

Study: Occasional pot smoking not as damaging as cigarettes

Science has shown the dangers of cigarette smoking on lungs– smoking undermines lung function, causes lung cancer and long-term breathing problems such as chronic obstructive pulmonary disease (COPD).  But what about smoking marijuana?

Researchers sought to determine whether exposure to marijuana smoke, which contains many of the same components in cigarette smoke, would also show negative effects on lung function.

They were surprised to find that subjects who occasionally smoked pot – meaning two to three times per month – did not show the same reduced lung function that was seen in cigarette smoking. The study was published in the Journal of the American Medical Association.

Using data from a 20 year study designed to measure heart disease called the Coronary Artery Risk Development in Young Adults (CARDIA) study, researchers analyzed data from more than 5,000 men and women, aged 18 to 30, from four U.S. cities.

Participants from Oakland, Chicago, Minneapolis and Birmingham were repeatedly measured for pulmonary function, height, smoking behavior, and waist circumference and asked about cigarette and marijuana smoking during each assessment.

“There are well known effects of tobacco on pulmonary function and we thought, going into this, that we would find similar types of effects for marijuana,” said lead study author Dr. Mark J. Pletcher of the University of California, San Francisco.

As expected, his team found among cigarette smokers, the more smoke a subject was exposed to, the more adverse effects they had in lung function. Lung function was measured with spirometry testing, which shows the amount of air a person can forcibly exhale, giving  doctors a measure of how well the lungs are functioning.

But Pletcher notes that his team was surprised to find that subjects who smoked limited amounts of marijuana actually were able to blow large volumes of air into the spirometer. 

“People who smoke marijuana inhale very deeply, which may strengthen the muscles used for inhalation – basically making them good at the test. So even though it’s a very statistically significant result, it probably doesn’t have any physiologic meaning in terms of function,” he explained. 

Subjects who smoked larger amounts of marijuana, which Pletcher described as smoking one joint per day, did show evidence of reduced pulmonary function, and he stressed that his study results are not intended to encourage people to use marijuana. 

However, for patients for whom medical marijuana may be a treatment option, the authors write that "marijuana may have beneficial effects on pain control, appetite, mood, and management of other chronic symptoms.  Our findings suggest that occasional use of marijuana for these or other purposes may not be associated with adverse consequences on pulmonary function.  It is much more difficult to estimate the potential effects of regular heavy use... our findings do suggest an accelerated decline in pulmonary function with heavy use."

It’s important to note that the findings of this study are not meant to encourage marijuana smoking, nor did the study examine other known negative effects of marijuana use, which include problems with memory, concentration and perception.

Marijuana is the most commonly used illegal drug in the United States, according to the National Institute on Drug Abuse. Long term use of marijuana can lead to addiction, and chronic marijuana use is associated with mental health problems including anxiety and depression. Studies have shown that when marijuana use begins at a younger age, it may increase mental health problems, including psychosis, according to NIDA.

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