Long-term marijuana use can affect lung health, but the impact depends heavily on how cannabis is used (smoked, vaped, or non-inhaled), how often, and whether tobacco is also involved. The strongest and most consistent signal in research is that regularly smoking cannabis irritates and injures the airways, leading to symptoms that look a lot like chronic bronchitis.
Public health agencies note that smoked cannabis can harm lung tissue. Summaries of the evidence describe how marijuana smoke can cause injury to the lungs, including airway irritation and damage consistent with inflammation and scarring. Respiratory health organizations similarly state that marijuana smoke can injure airway linings and is linked with chronic bronchitis symptoms—notably chronic cough, phlegm or mucus production, wheezing, and episodes of acute bronchitis.
Large evidence reviews have concluded there is substantial evidence that long-term cannabis smoking is statistically associated with worse respiratory symptoms and more frequent chronic bronchitis episodes, and that stopping cannabis smoking is likely to reduce these bronchitis-type symptoms over time. For consumers, the practical takeaway is straightforward: even if a person never touches tobacco, repeatedly inhaling hot combusted smoke can inflame airways, increase mucus production, and make breathing feel “heavier” during exercise or at night.
Where the science becomes more nuanced is in lung function testing, such as standard spirometry measures. Some long-running cohort studies have not found the same clear, progressive decline in certain lung function measures seen with tobacco at typical exposure levels, though patterns such as changes in lung volumes and ratios have been reported and interpreted in different ways. This does not negate symptoms; it means that persistent cough, wheeze, and phlegm can occur even when certain clinical lung-function numbers do not show a dramatic drop.
Other potential downsides appear more likely in heavy or high-risk use patterns. Frequent deep inhalation and breath-holding can increase exposure to tar and airway irritants. Clinical reports have also described complications such as air-trapping, large lung bullae, and spontaneous pneumothorax (collapsed lung) in some heavy users, though overall population risk is less clearly quantified than with long-term tobacco smoking. Evidence linking cannabis smoking to lung cancer remains mixed and difficult to interpret, particularly because many users also smoke tobacco; current reviews generally describe the association as inconclusive rather than definitive.
Finally, inhaling cannabis via vaping is not inherently risk-free. Severe lung injuries associated with some THC vaping products—particularly those obtained from informal or unregulated sources—have highlighted the dangers of inhaling contaminated aerosols.
For consumers concerned about respiratory health, the most evidence-based harm-reduction strategy is limiting or avoiding inhalation altogether, choosing regulated non-inhaled options where legal and appropriate, and seeking medical advice for persistent respiratory symptoms or preexisting lung conditions.