Several substances besides tobacco are inhaled for recreational purposes, including marijuana, crack cocaine, amyl and butyl nitrites, heroin, methamphetamine, and phencyclidine. Abuse of most of these inhaled substances has risen in recent years, thereby increasing concern about potential pulmonary and other medical complications. Regular marijuana use can lead to extensive airway injury and alterations in the structure and function of alveolar macrophages, potentially predisposing to pulmonary infection and respiratory cancer. Crack cocaine use can lead to a variety of acute pulmonary complications, including severe exacerbations of asthma and an acute lung injury syndrome associated with a broad spectrum of histopathologic changes (“crack lung”). Habitual cocaine smoking may also produce more subtle long-term pulmonary consequences due to chronic alveolar epithelial and microvascular lung injury. Heroin inhalation can induce severe and even fatal exacerbations of asthma. Pulmonary consequences of inhaled amyl and butyl nitrites, crystalline methamphetamine (ice), and phencyclidine have been less well documented.