Marijuana smokers are slightly more likely to develop lung disease than cigarette users, a shock study suggests.

Researchers looked at roughly 150 adults in Canada who were about 50 years old on average and were either pot users, tobacco smokers or non-smokers.

Three-quarters of marijuana users had emphysema – a lung disease which laves sufferers struggling to breathe – compared to two-thirds of tobacco users.

Just one in 20 non-smokers suffered from the condition, which kills more than 120,000 Americans each year.

Study author Dr Giselle Revah, a cardiothoracic radiologist and assistant professor at the University of Ottawa, said she was surprised by the results.

She said the findings suggest ‘marijuana has additional synergistic effects on the lungs above tobacco’.

The researchers said tobacco cigarettes are usually filtered, whereas marijuana is smoked unfiltered, meaning that more irritants reach the airways. 

One of the limits of the study was that most cannabis users were also either current or former tobacco smokers – meaning the damage might have already been done.

The study also didn’t distinguish between joint or blunts — joints are purely marijuana whereas blunts also contain tobacco.

The findings come amid a wave of legalizations, including Maryland and Missouri just last week, with 21 states now allowing recreational use. A further eight allow it for medical reasons.


Marijuana smokers are more at risk of lung disease, as well as breathing problems and chronic bronchitis, Dr Giselle Revah's team found

Marijuana smokers are more at risk of lung disease, as well as breathing problems and chronic bronchitis, Dr Giselle Revah’s team found 


Chronic obstructive pulmonary disease (COPD) describes a group of lung conditions that cause the airways to narrow and become inflamed.

Examples include bronchitis, which affects the airways, and emphysema, which impacts the air sacs. 

This makes it harder to move air in and out as you breathe.

Around 1.2million people in the UK are diagnosed with COPD, British Lung Foundation statistics show. 

And in the US, 16million people suffer from COPD, according to the Centers for Disease Control and Prevention. 

It usually develops due to long-term damage to the lungs from smoking or air pollution.

Jobs where people are exposed to fumes, dust and chemicals also raise the risk. 

COPD also seems to run in families.

And a rare genetic condition called alpha-1-antitrypsin deficiency makes people susceptible at a very young age.  

Symptoms include:

  • Breathlessness during day-to-day activities, like walking
  • Persistent cough
  • Wheezing in cold weather
  • Producing excess phlegm

In severe cases, sufferers lose their appetite, have swollen ankles, lose weight and may even cough up blood. 

COPD is incurable and the damage to the lungs cannot be reversed. 

However, treatments can help make breathing easier. 

Patients should also quit smoking and maintain a healthy weight. 

Marijuana is the most popular psychoactive substance in the world, and the second most-smoked substance after tobacco.

According to the Center for Disease Control and Prevention (CDC), marijuana is the most widely used federally illegal drug in the US, and 18 per cent of Americans used it at least once in 2019. 

Marijuana smoke contains many of the same toxins as tobacco smoke, and it can harm lung tissues and damage and scar small blood vessels, the CDC says.

Weed has overtaken cigarettes in the US now, with only 13 per cent of US adults using them in 2020.

Dr Revah said: ‘Our marijuana smokers — some of whom also smoked tobacco — had additional findings of airway inflammation/chronic bronchitis [which] suggests that marijuana has additional synergistic effects on the lungs above tobacco.’

In the latest study, researchers from the University of Ottawa compared chest CT scans of 56 marijuana smokers with 57 non-smoking controls and 33 tobacco-only smokers.

Fifty of the 56 marijuana smokers also smoked tobacco.

They found that 75 per cent of the marijuana smokers had emphysema, in contrast to 67 per cent of those who only smoked tobacco.

Of the non-smokers, only 5 per cent had emphysema.

Paraseptal emphysema was the main type of emphysema the researchers found in marijuana smokers, where tiny ducts connecting air sacs in the lungs become damaged.

Inflammation of the airways and gynecomastia — enlarged male breast tissue due to an imbalance of hormones — were also more prevalent in marijuana smokers than non-smokers.

Gynecomastia was found in 38 per cent of marijuana smokers, but only 11 per cent of tobacco smokers.

Meanwhile, 16 per cent of the control group had enlarged male breast tissue.

Marijuana can cause the side effect by  acting as an estrogen stimulator. 

UFC fighter Israel Adesanya suffered very noticeable gynecomastia on his left breast last year and blamed it on weed overuse – but doctors said it was more likely to be a sign of steroid abuse.

The study found no difference in coronary artery calcification – a build up of calcium which can be an early sign of coronary artery disease – between age-matched groups of marijuana smokers and tobacco-only smokers.

Dr Revah said the results were surprising, particularly because patients in the tobacco-only group had been smoking for a long period of time.

She said: ‘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.

‘In addition, our results were still significant when we compared the non-age-matched groups, including younger patients who smoked marijuana and who presumably had less lifetime exposure to cigarette smoke.’

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

More breathing problems could be due to the way marijuana is smoked. Marijuana tends to be inhaled for longer than tobacco smoke.

Dr Revah suggested further research could investigate the effects of different inhalation styles, such as through a bong, a joint or a pipe.

The findings were published in the journal Radiology.

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