Introduction Inhaled marijuana has been infrequently identified as a potential risk factor for the development of spontaneous pneumomediastinum (SPM), a rare finding of free air in the mediastinum likely caused by barotrauma during breathing manoeuvres. The mechanism of inhalation drug use is often not ascertained by physicians, thus little is known about how different smoking techniques precipitate pulmonary injury. We aimed to evaluate the frequency of marijuana use in patients with non-traumatic pneumomediastinum over a 12-month period, identifying additional relevant clinical features or risk factors, and determining the extent to which clinicians record smoking techniques.

Methods We performed a retrospective chart review over a 1-year period, identifying patients presenting to the hospital with a diagnosis of pneumomediastinum in the absence of trauma, malignancy or iatrogenic cause.

Results We identified 21 cases, 14 of which (66.7%) were associated with marijuana use, average age was 22.5 years (range 18–30), with male predominance (64.2%). Daily or more use was reported in 50% of cases. Concurrent risk factors including vomiting (57.1%) and coughing (42.9%) were commonly present. The mechanism of smoking was described in only two cases (14.3%).

Discussion Inhaled marijuana may be an underappreciated risk factor for the development of SPM, caused by air leakage around the bronchovascular sheaths during successive inhalation through a high-resistance smoking apparatus or forced exhalation against a closed glottis. Physicians should be aware of this association in order to provide appropriate counselling. Further research is needed to direct the safe use of smoking devices and techniques.