In the 5,000-or-so years that humans have been smoking up, not one credible piece of evidence has emerged proving cannabis use is seriously bad for our health, either in the short term or over a lifetime.

Marijuana ScientistThat’s partly because very little research has been conducted into the true safety of weed. The studies that do exist suggest little more than unexplained correlations between pot use and some health problems. None have uncovered evidence that marijuana actually causes any of those problems.

But that doesn’t mean that every important question has been answered. A new study, released in January, could help shut the door on a big lingering mystery: Does long-term toking cause lung disease?

Researchers at Emory University in Atlanta studied the effects of regular marijuana smoke on lung health in a large group of American adults between 18 and 59 years old. They compared adults with varying lengths of use, measured in “joint years,” or the number of years during which a person smokes 365 joints.

No major decline in lung function

A stoner who tokes one joint a day for one year would thus have one joint year. A stoner who tokes two joints a day for the same year would have two joint years. The study found that potheads with 20 or more joint years didn’t see any major decline in lung function.

Specifically, two common breath tests revealed no loss in forced expiratory volume and no drop in breath measurement values in diseases of the small airways. This means that weed appears to be far safer for the lungs than tobacco, which is well known to cause terminal lung cancer and other severe breathing disorders.

“The pattern of marijuana’s effects seems to be distinctly different when compared to that of tobacco use,” the researchers wrote. The study was released online in advance of its publication in the Journal Annals of the American Thoracic Society.

The authors did have a warning for potheads: Heavy toking can lead to chronic bronchitis.

“In a large representative sample of U.S. adults, ongoing use of marijuana is associated with increased respiratory symptoms of bronchitis, without a significant functional abnormality in spirometry, and cumulative marijuana use under 20 joint-years is not associated with significant effects on lung function,” the authors wrote. Spirometry is the measurement of breath function.

Less harmful than cigarettes

Obviously no one wants bronchitis, especially the chronic kind, but it’s insignificant compared to the dangers of cigarette smoking. Tobacco is easily one of the world’s deadliest substances, while the historical record doesn’t contain a single credible report of death by marijuana.

What’s more, the weed industry is adapting to concerns about bronchitis and lung irritation by offering a wide range of vaporizers. Inhaling water vapor containing THC is generally thought to be safer than smoking the drug.

marijuana leavesAn earlier study, published three years ago in The Journal of the American Medical Association, likewise found that as many as seven joint years (seven years of one joint per day) had no significant adverse effects on lung function.

Another study, from 2013, found that long-term heavy pot smoking doesn’t lead to lung cancer, chronic obstructive pulmonary disease, bullous lung disease, or emphysema.

“Habitual use of marijuana alone does not appear to lead to significant abnormalities in lung function,” the authors of that study reported. “Findings from a limited number of well-designed epidemiological studies do not suggest an increased risk of either lung or upper airway cancer from light or moderate use … Overall, the risks of pulmonary complications of regular use of marijuana appear to be relatively small and far lower than those of tobacco smoking.”

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