Evidence collection for cannabis effect on the lung is complicated by issues of accurately understanding the dose given, the concomitant use of nicotine making the effect of the cannabis difficult to assess, and the evidence mostly including only THC while CBD is getting more common to be used for medicinal purposes.

Smoking THC is associated with worsening respiratory symptoms of cough or sputum, wheezing, and shortness of breath, increased incidence of acute bronchitic episodes or clinic visits for acute respiratory illness.

Cannabis leads to hyperinflation and increased large airway resistance, with little evidence of airflow obstruction (cf. nicotine smoking, which causes airflow obstruction).

The association of smoking cannabis to lung cancer risk is not clear.

Multiple case reports show a relationship of cannabis smoking to multiple respiratory conditions including cannabis-induced complications including aspergillosis, hemoptysis, emphysema and secondary pneumothorax, hypersensitivity pneumonitis, eosinophilic pneumonitis, ARDS, vanishing lung syndrome, and emphysema.