Chronic obstructive pulmonary disease (COPD) is common among people who use illicit opioids. This study will estimate the incidence of diagnosed COPD and the rate of death due to COPD among patients in primary care in England with previous records of illicit opioid use, and compare this to patients without records of illicit opioid use. Among patients with a new COPD diagnosis, we estimate the association between illicit opioid use and the probability of preventative healthcare such as flu and pneumococcal vaccines or support with smoking cessation, and the association between illicit opioid use and adverse outcomes such as acute exacerbations and death. Data will be drawn from the Clinical Practice Research Datalink (CPRD), using a validated method to identify patients with a history of illicit opioid use. Patients without a history of illicit opioid use will be selected using a process called ‘exposure density sampling’ to create a cohort matched on age, sex, GP practice, and date of cohort entry.