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Marijuana Less Damaging to Lungs Than Tobacco

Thursday, January 12, 2012


Good news for the hemp community: marijuana not as harmful to lungs as tobacco.

A large-scale national study suggests low to moderate use of marijuana is less harmful to users’ lungs than exposure to tobacco, even though the two substances contain many of the same components. This comprehensive study, led by University of California San Francisco and University of Alabama at Birmingham, collected data from more than 5,000 US adults for more than 20 years.

Smoking cigarettes can cause significant lung damage, including respiratory symptoms, chronic obstructive pulmonary disease and lung cancer. It accounts for an estimated 443,000 deaths, or nearly one in every five deaths, each year in the United States, according to the Centers for Disease Control and Prevention (CDC). Data for the long-term effects of marijuana use on the pulmonary system has been scarce until now.

“We found exactly what we thought we would find in relation to tobacco exposure: a consistent loss of lung function with increasing exposure,” said the paper’s lead author, Mark Pletcher, MD, MPH, associate professor in the Division of Clinical Epidemiology at UCSF. “We were, however, surprised that we found such a different pattern of association with marijuana exposure.”

First major study to look at marijuana 

In a paper published yesterday in the Journal of American Medical Association (JAMA), researchers analyzed the relationship between current and lifetime exposure to marijuana and pulmonary function. The Coronary Artery Risk Development in Young Adults (CARDIA) study collected medical data from 5,115 men and women in four U.S. cities from 1985-2006.

They measured air flow rate – the speed in which a person can blow out air – and lung volume, which is the amount of air a person is capable of holding, typically about six liters of air for an adult male. Lung function was measured using a common medical device called a spirometer that measures air flow when the participant breathes in and out.

Tobacco: the more you use, the more loss you have

“Essentially with tobacco, the more you use, the more loss you have with both of the indicators, air flow rate and lung volume,” said the paper’s last author Stefan Kertesz, MD, MSc, associate professor in the Division of Preventive Medicine at the University of Alabama at Birmingham School of Medicine and the Birmingham VA Medical Center. “There’s a straight-line relationship: the more you use, the more you lose.”

The same was not true with marijuana use. Air flow rate increased rather than decreased with increased exposure to marijuana up to a certain level.

Amount plays a role

“An important factor that helps explain the difference in effects from these two substances is the amount of each that is typically smoked,” Pletcher said. “Tobacco users typically smoke ten to 20 cigarettes/day, and some smoke much more than that. Marijuana users, on average, smoke only two to three times a month, so the typical exposure to marijuana is much lower than for tobacco.”

“And marijuana is one where a lot of people dabble with it in their late teens and 20s, and some people continue with relatively low levels for a long period of time,” Kertesz added.

Expert response from RI Hospital

GoLocalProv asked Douglas W. Martin, MD, department of Pulmonary, Critical Care, and Sleep Disorder Medicine at Rhode Island Hospital, about the implications of this high-profile research finding.

How valid is this study?

This study attempted to answer a question which is difficult to study within the constraints of time and ethical, responsible research. They wanted to assess both acute and chronic effects of marijuana use on lung function, and this is not amenable to the gold standard to prove causation in medicine of a randomized controlled trial. As a result, they needed to employ a wide range of statistical techniques, and these can always impact the validity of a study’s conclusions.

With those caveats, this study does suggest that low level marijuana use amongst a young, healthy population does not adversely affect lung function (on either a short or long term basis). One of the nice things about this trial was the number of subjects studied and the number of years over which they were studied (up to 20).

Is this something you will be paying attention to?

Absolutely. Marijuana has obviously received a lot of attention for its potential therapeutic effects in a wide range of chronic medical conditions. Delineating the potential adverse effects of heavier, more chronic use will be important in counseling these patients.

What are the implications for marijuana use, going forward?

I think that this study adds to the limited literature which suggests that low level marijuana use amongst young, healthy people probably has little to no long term effects on lung function. It is important to recognize that the average age in this study was 25 and it only examined lung function in Caucasians and African Americans. It also was not designed to study other potential pulmonary sequelae of marijuana use.

Anecdotally, we have seen a number of fairly young people diagnosed with lung cancer with a history of heavy marijuana use and little to no history of tobacco use. In addition, patients with chronic immune problems or those on chemotherapeutic agents may be at higher risk of respiratory fungal infections which can sometimes develop in marijuana users. Given that older, sicker patients are sometimes the ones using marijuana for therapeutic purposes, I’m not sure that this study adds much to the knowledge base regarding the potential adverse health effects they could face. In fact, these researchers did find a trend towards reduced lung function with chronic, heavy use of marijuana.

What can RIers take away from this new information?

I think that RIers can take away the knowledge that occasional (1-2x/month) marijuana use in fairly young and healthy people probably is not going to increase their risk of diseases such as emphysema in a significant manner. While marijuana and tobacco have some of the same components, most people do not smoke nearly as much marijuana as they would tobacco. This study did show a significant, linear reduction in lung function with chronic cigarette use, and chronic heavy use of marijuana may pose similar risks. Extrapolation of the results of this study to patients who are older or have pre-existing pulmonary or other chronic illnesses is fraught with potential problems.

The study was supported by funds from the National Heart Lung Blood Institute.  

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