Does Cannabis Smoke Cause Interstitial Lung Disease?

<b>Background/Objectives</b>: The correlation between drugs and interstitial lung disease (ILD) is reported, but the presence of the substances of abuse in the lung as a cause of disease has never been proved. In this observational study, our aim was to evaluate a possible correlation between ILD radiological findings and cannabinoids presence in broncho-alveolar lavage (BAL) or in resected lung tissue in patients with a history of cannabis smoke. <b>Methods</b>: Data of patients with ILD chest CT scan findings and history of drug use, submitted to BAL (Group 1), or to lung apex removal for pneumothorax (Group 2), were retrospectively collected. In both groups, drug presence was investigated. A subgroup of Group 1 was checked for the concomitant presence in blood. Fisher's test was used to study the association between the detection of the drug and ILD. <b>Results</b>: In Group 1, cannabinoids were present in 12/26 (46.2%) BAL samples. ILD emerged on chest CT in 75% of the cannabinoid-positive and in 20% of the cannabinoid-negative BAL samples (<i>p</i> = 0.0299). In the subgroup, the patients who tested positive for cannabinoids/cocaine on BAL were 55.6%; 0% were positive only on blood (<i>p</i> = 0.0294). In Group 2, cannabinoids were present in 10/15 (66.7%) specimens. ILD was evident, respectively, in 40% and in 0% of the patients with cannabinoid-positive and cannabinoid-negative surgical specimens (<i>p</i> = 0.2308). <b>Conclusions</b>: The prevalence of ILD in patients with cannabinoid-positive BAL and in those with cannabinoid-positive surgical specimens suggests that ILD could be caused by cannabis smoke. The non-concomitant presence of substances in BAL and in blood advocates the diagnostic usefulness of searching for the drug in the target organ.