Hulin J, et al. - Researchers sought to compile the evidence relating illicit opioid use with poor respiratory health via performing a systematic review of the literature in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidance. Exploring MEDLINE, Embase, PsycINFO, CINAHL and the Cochrane Library databases they included studies (English language, published January 1980–November 2018) conducted in community and hospital settings in the United States (n = 23), United Kingdom (n = 7), Australia (n = 7), the Netherlands (n = 2), Canada (n = 2), Ireland (n = 1), Spain (n = 1) and Iran (n = 1). As per meta-analyses, the estimated prevalence of asthma was 8.5% in people who inject illicit opioids and was 20.2% in people who inhale illicit opioids. The prevalence of chronic obstructive pulmonary disease was estimated as 2.7% in people who inject illicit opioids and as 17.9% in people who inhale illicit opioids. These findings suggest the heightened burden of respiratory diseases in people who use illicit opioids. As the study design and samples were heterogeneous, accurate estimates of the prevalence of the respiratory disease in this population seemed difficult to gain.