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Researchers say heavy cannabis use can cause lung damage as well as lead to mental health issues. Getty Images
  • Researchers say heavy cannabis use can lead to respiratory ailments such as bronchitis and “bong lung.”
  • They add, however, there is no evidence that cannabis use causes serious diseases such as cancer or chronic obstructive pulmonary disease (COPD).
  • Other researchers say heavy cannabis use can increase the risk of mental health issues.

Recent studies from universities in New Zealand and England conclude that cannabis smoke may be more hazardous to humans than previously known.

Researchers from New Zealand’s University of Otago say smoking cannabis in heavy amounts can lead to bronchitis and irreversible lung damage, also known in some circles as “bong lung.”

“The bronchitis that people get, the really nasty bronchitis, does tend to improve if you stop [cannabis use],” Bob Hancox, a respiratory specialist and research professor at Otago as well as an author of the recent study, told Radio New Zealand. “But what we, as lung doctors, see in people that don’t stop smoking cannabis, we see people coming in with lungs which are very, very badly damaged with lots of destruction of the lung tissue, and that is irreversible.”

In separate research, researchers from England’s University of Bristol said users of high potency cannabis are four times more likely to report associated health problems and twice as likely to report having an anxiety disorder.

“We know that people who use cannabis are more likely to report mental health problems than those who don’t use cannabis, but we don’t fully understand how recent increases in the strength and potency of cannabis affects this,” Lindsey Hines, PhD, a research associate at Bristol and lead study author, said in a statement. “This study gives us an estimate of the increased likelihood of mental health problems from use of high potency cannabis, compared to use of lower potency cannabis.”

Cannabis is sometimes used to treat symptoms from a number of health issues, including cancer, glaucoma, multiple sclerosis, Crohn’s disease, and mental health conditions such as schizophrenia and post-traumatic stress disorder.

Scientists say the effects of cannabis on lung health has been difficult to isolate, as users frequently smoke tobacco as well.

They add it’s also difficult to study because the strength and ingredients of cannabis vary.

According to the Otago study, cannabis is one of the world’s most widely used recreational drugs and the second most commonly smoked substance.

“The pattern of effects is surprisingly different from that of tobacco,” the researchers wrote. “Whereas smoking cannabis appears to increase the risk of severe bronchitis at quite low exposure, there is no convincing evidence that this leads to chronic obstructive pulmonary disease (COPD).”

“Instead, cannabis use is associated with increased central airway resistance, lung hyperinflation, and higher vital capacity with little evidence of airflow obstruction or impairment of gas transfer,” they added.

While smoking tobacco has been found to cause cancer and COPD, the researchers concluded there isn’t enough evidence to say the same about cannabis.

“An association between cannabis and lung cancer remains unproven, with studies providing conflicting findings,” the researchers said.

“We are still clearly trying to determine if cannabis smoking definitely causes irreversible lung damage and, if so, what makes people more susceptible to lung damage,” Carey S. Clark, PhD, chair of the Medical Cannabis Program at Pacific College of Health and Science in San Diego, told Healthline. “We also are not sure if certain illnesses may lead to more lung issues with inhaling cannabis, as in the case of asthma being diagnosed in a higher percentage with cannabis smokers.”

John Docherty is the president of Lexaria Bioscience, a Canadian pharmaceutical company that has researched the effect of cannabis on lungs.

He told Healthline that inhalation volumes among cannabis users are usually larger than those of nicotine users.

He said cannabis users generally hold their breath four times longer and take in five times the concentration of carboxyhemoglobin formed in carbon monoxide poisoning.

“Smoking is not a healthful means of delivering drug substances to the body and should be avoided whenever possible, except in the instances when therapeutic drugs are being delivered to treat pulmonary disease conditions,” Docherty said. “These findings are especially critical in this time of a worldwide health pandemic such as COVID-19, where numerous researchers have noted that the chronic lung inflammation demonstrating with smoking is conducive to a poorer prognosis in the event individuals become infected with COVID-19.”

Clark said the study shows more research is needed.

“There has been a stigma created around cannabis, and many people believe it can only be smoked. The benefit in inhaled cannabis is that it acts more immediately and for those suffering from pain and nausea, this effect can bring about more timely relief of symptoms,” she said. “Cannabis can also be ingested in the form of tinctures, included in edibles, and applied topically. It is a medicine and people should be taught how to use it safely and effectively while minimizing the risks, as cannabis does have side effects and potential adverse effects.”

The University of Bristol study focused on the effects of cannabis on more than 14,000 children born during the 1990s in and around Bristol in southwest England.

Researchers looked at data from a general population sample and considered whether mental health issues in mothers were apparent before the use of cannabis. Researchers concluded that reducing the potency and regularity of cannabis use lessens the likelihood of harm.

“In countries where cannabis is sold legally, limiting the availability of high potency cannabis may reduce the number of individuals who develop cannabis use disorders, prevent cannabis use escalating to a regular behavior, and reduce impacts on mental health,” Hines said in a statement. “In countries like the U.K., where we are not able to limit the availability of high potency cannabis, we should make sure there is good treatment and support for those who develop problems from cannabis use.”