The prevalence and impact of cannabis smoking in clinical trial patients with chronic obstructive pulmonary disease

Introduction: Cannabis is the most commonly used illicit drug worldwide. Despite this little understanding exists of the lung function or health status impact and is often overlooked at clinical trial screening. Aims: To assess the prevalence and impact of cannabis smoking in chronic obstructive pulmonary disease (COPD) trial patients. Methods: Between November 2012-August 2014, 45 stable hyperinflated COPD patients were randomised into a single centre clinical trial and underwent lung function and symptom scoring at baseline. Furthermore they had a thorough cigarette and cannabis history taken. Results: 8/45 (18 %) of patients recruited reported having previously smoked cannabis (cumulative dose 7.81±3.40kg) in combination with tobacco without filters. They were younger (55±8 vs 66±8yrs) and had a male predominance (100 vs 56%) with a similar cigarette smoking history compared to the rest of the cohort. There were no differences in percent-predicted forced expiratory volume in 1s (49.9 vs 48.8, p=0.86) or percent-predicted residual volume (190±47 vs 168±38, p=0.14), although there were trends in reduced gas transfer (KCO% 53±12 vs 70±21, p=0.06). Although they had similar dyspnoea scores, the use of cannabis was associated with a worsening of health status (COPD Assessment Test score (25.4±4.6 vs 17.0±8.5, p=0.01). Conclusions: The use of cannabis in combination with tobacco is a common finding in trial participants and predisposes users to a diagnosis of COPD at an earlier age, poorer health status and a trend towards poorer lung function. Clinical trial participation therefore provides an opportunity to provide counselling and behaviour change in this cohort.