Vaporized cannabis did not help breathing or exercise endurance in people with severe COPD

This was a randomized controlled trial of 16 adults with advanced COPD (mean FEV1 36% predicted). Participants inhaled 35 mg of vaporized cannabis (18.2% THC, less than 0.99% CBD) or control. Outcomes included breathlessness during cardiopulmonary exercise testing, exercise endurance time, resting lung function (spirometry and impulse oscillometry), cognitive function, psychoactivity, and mood.

Some people with COPD use cannabis hoping it will help their breathing, partly based on old studies showing bronchodilatory effects in other populations. This rigorous trial found that those earlier findings do not translate to advanced COPD. The null result is itself important information, as it helps patients and clinicians make informed decisions.

This study fills a specific gap in the literature, testing whether the bronchodilatory properties of cannabis observed in healthier populations hold up in advanced lung disease. The negative result suggests that the degree of airway disease in COPD may be too severe for cannabinoid-mediated bronchodilation to provide meaningful benefit, or that different mechanisms are at play in COPD versus asthma.

The sample was very small at 16 participants. Only a single dose was tested, and chronic effects might differ. The cannabis used had very low CBD content, and CBD may have different respiratory effects. Only advanced COPD was studied, and results might differ in mild or moderate disease. The study design was acute rather than looking at longer-term outcomes.