This study aims to asses the influence of inhalable heroin on pulmonary function in chronic heroin-dependent patients treated with inhalable heroin. Among 32 patients (all cigarette smokers), a spirometric test was conducted at baseline and after an average period of 10 months of treatment with medically prescribed heroin. Patients showed a high frequency of pulmonary dysfunction at baseline [34%, with percentage of forced expiratory volume in 1 s (%FEV<sub>1</sub>) <80%]. However, after excluding those who started pulmonary treatment (n = 2) or who used heroin intravenously only (n = 2), no statistically significant differences in %FEV<sub>1</sub> between baseline and follow-up were observed (n = 28; mean %FEV<sub>1</sub> 86% at baseline vs. 91% at follow-up; p = 0.09). This small and relatively brief study suggests that 10 months of co-prescribed inhalable heroine base does not seem to (further) deteriorate pulmonary function in chronic, cigarette smoking treatment refractory heroin addicts. Screening for and treatment of pulmonary dysfunction is recommended for methadone patients with and without co-prescribed heroin.