The link between smoking tobacco and lung disease is undeniable, but what about smoking marijuana? A new Canadian study reached a surprising conclusion. It found that marijuana smokers are more likely to develop airway inflammation (which can lead to bouts of bronchitis and asthma), as well as emphysema, a lung condition that causes shortness of breath, than cigarette smokers.

Marijuana, also known as weed, herb, pot, grass, bud, ganga, MaryJane and other slang terms, is made from the buds and leaves of the cannabis plant. These parts of the plant are dried and either smoked as a cigarette or in a pipe, or consumed in edible forms.

People consume marijuana in order to alter their state of consciousness, relax or to help with a number of medical conditions including relieving chronic pain and sleep problems. It’s one of the most popular psychoactive substances used around the world, and the second most commonly smoked substance after tobacco. To date, it’s legal in 21 states.

Airway inflammation was more common in marijuana smokers than tobacco smokers and non-smokers.

“We know what cigarettes do to the lungs,” the study’s author, Giselle Revah, a cardiothoracic radiologist and assistant professor at the University of Ottawa in Ottawa, Canada, said in a press release. “There are well researched and established findings of cigarette smoking on the lungs. Marijuana we know very little about.”

To find out more, she and her colleagues compared chest CT results from 56 marijuana smokers, 33 tobacco-only smokers and 57 non-smoking control participants.This is what they found:

  • Three quarters of the marijuana smokers had emphysema, compared with 67 percent of the tobacco-only smokers. Only 5 percent of non-smokers had emphysema.
  • Airway inflammation was more common in marijuana smokers than tobacco smokers and non-smokers.
  • Enlarged male breast tissue due to a hormone imbalance (called gynecomastia) was found in 38 percent of the marijuana smokers, compared with 11 percent of the tobacco-only smokers and 16 percent of the controls.

“The fact that our marijuana smokers — some of whom also smoked tobacco — had additional findings of airway inflammation/chronic bronchitis suggests that marijuana has additional synergistic effects on the lungs above tobacco,” Revah indicated.

But what’s the reason for this greater lung damage from marijuana smoking? It might be because weed is most often smoked in a non-filtered, self-rolled “joint”, while cigarettes are usually filtered, so more toxic particulates are inhaled into the lungs with the joint. What’s more, marijuana is inhaled with a longer breath hold and so-called “puff-volume” than cigarette smoke.

“It has been suggested that smoking a marijuana joint deposits four times more particulates in the lung than an average tobacco cigarette,” Revah said. “These particulates are likely airway irritants.”

You may want to consume marijuana through edibles or smoke it using a bong or water pipe, though whether bongs are safer for your lungs is not yet clear.

Even if you haven’t developed respiratory symptoms, but you’re a marijuana smoker and want to know whether you are damaging your lungs, your doctor can identify early-stage lung disease by having you take a pulmonary function test. Lung function can be measured non-invasively with a spirometer — a device that you use as you breathe in and out based on specific instructions by your healthcare provider. A spirometer measures the volume of air that you inhale and exhale at timed intervals.

Practicing deep breathing may help to keep your lungs healthier. Here’s how to do it:

    1. Lie comfortably on your back in bed or on the floor with a pillow under your head and knees.
    2. Breathe in through your nose. Let your belly fill with air.
    3. Breathe out through your nose.
    4. Place one hand on your belly.
    5. As you breathe in, feel your belly rise. As you breathe out, feel your belly relax.
    6. Take three more full, deep breaths.

The study is published in Radiology.