MONDAY, July 2, 2018 (HealthDay News) -- Smoking marijuana once a week can cause coughing, wheezing and phlegm, all signs of chronic bronchitis, a new evidence review reports.
Pot smoking doubles a person's risk of developing a regular hacking cough. It also triples the risk of coughing up phlegm and suffering from wheezy constricted breathing, researchers found.
"We know that smoke from tobacco and other entities -- including burning wood in your fireplace -- causes chronic bronchitis, so it's not at all surprising they found chronic bronchitis in prior marijuana research," said Dr. Norman Edelman, senior scientific adviser to the American Lung Association.
Edelman said he's concerned that heavy marijuana use could lead to larger health problems for those who develop chronic bronchitis.
"You would worry about people being more susceptible to pneumonia, and of course, the end result of chronic bronchitis, if it persists long enough and is severe enough, is what we call COPD -- chronic obstructive pulmonary disease," Edelman said.
About half of tobacco smokers get COPD, he said. "It will be interesting to see what percentage of regular marijuana smokers get COPD," he added.
Paul Armentano, deputy director of NORML, a group supporting reform of marijuana laws, said the study findings are "consistent with prior data."
"It is hardly surprising that the habitual inhalation of combustive smoke may be associated with specific, though generally mild respiratory symptoms, like cough," he said.
"However, unlike the inhalation of tobacco smoke, cannabis smoke exposure -- even long-term -- is not associated with the kind of serious respiratory effects that are often identified with long-term tobacco use, such as COPD, emphysema or lung cancer," Armentano said.
About 13 percent of adults and 21 percent of young adults are believed to be regular pot users.
Marijuana legalization has led to the development of many alternatives to smoking pot, such as cannabis-infused edibles, oils and concentrates, Armentano said.
For the evidence review, researchers led by Dr. Mehrnaz Ghasemiesfe, from the San Francisco VA Medical Center, analyzed data from 22 studies of the effects of pot smoking on lung health.
Analysis of two prospective studies (ones that watch for outcomes such as disease development) found pot smoking associated with a doubled risk of cough and a nearly quadrupled risk of phlegm, the results showed.
Combined analysis of other studies revealed an increased risk of cough (4.3 times); phlegm (3.4 times); wheezing (2.8 times); and shortness of breath (1.5 times).
Some are concerned that as more U.S. states legalize pot, more people will develop lung problems.
"Because some of the worst effects of smoking take years to show effect, it took time until we had established clear and undeniable risks of cancer, heart disease and other major medical problems that were caused by smoking tobacco," said Dr. Adam Lackey, chief of thoracic surgery at Staten Island University Hospital in New York City.
"I worry that we are looking at a similar situation with marijuana," he said. "People need to realize that we just don't know yet what the long-term effect of marijuana smoking is. This study shows that marijuana smoking certainly isn't totally benign."
At the same time, Edelman, the lung association adviser, doubts marijuana will be as harmful as tobacco, simply because it's not smoked as much.
"My guess is that not many marijuana users smoke 20 joints a day, which would be equivalent to a pack a day for a cigarette smoker," he said.
"I don't think the smoke of marijuana is necessarily less toxic than the smoke of tobacco. It's just that in general, people who use marijuana smoke fewer marijuana cigarettes than people who smoke tobacco," Edelman said.
The new study was published July 2 in the Annals of Internal Medicine.
The American Lung Association has more about marijuana and lung health.