Designing greener participant centred trials: an analysis of 'carbon relevant' factors within items that influence participants decisions about trial recruitment and retention

The World Health Organization have recognised climate change as one of the biggest health threats facing humanity, considering its effects on social and environmental determining factors of health such as clean air, potable water, adequate food and secure shelter [1]. In 2007, the Sustainable Trials Study Group concluded that ‘clinical trials contribute to greenhouse gas emissions, and estimates in 2023 predicted that the 350,000 trials registered on ClinicalTrials.gov have a carbon usage of 27.5 M tonnes [2, 3]. Nevertheless, clinical trials are essential for identifying effective and safe treatments and preventing diseases. General recommendations targeting the reduction of carbon usage in research (National Institute for Health Research (NIHR) Carbon Reduction Guidelines) were published in 2019 yet progress to decarbonise trials remains slow [3, 4]. Of the small number of studies that have explored carbon usage in clinical trials, factors such as energy usage in research premises, trial team, and participant-related travel have been identified as key impacts [5, 6].

Efforts to deliver more environmentally sustainable research, including clinical trials, continue to gather pace both in academic and industry-led trials, in line with the acute growth of the climate threat worldwide [6]. A recent paper by Griffiths et al. developed a method and associated guidance to help trialists to efficiently estimate the carbon footprint of a clinical trial and, consequently, increase the trialists’ recognition of trial-specific carbon emissions and ability to enhance climate change mitigation [3]. One of the key considerations for clinical trials going forwards is to consider the trade-offs in design aspects with rigour and patient acceptability, e.g. reducing the number of in-person visits for follow-up to reduce the carbon footprint balanced against impacts on trial retention [6]. There is currently very little evidence as to what or whether carbon-relevant aspects of trials (e.g. patient travel, mode of data collection) influence patients’ decision-making in relation to trial participation. The findings outlined in this letter explore which ‘carbon relevant’ factors are related to previously identified factors influencing patients’ decision-making in relation to taking part (recruitment) and staying (retention) in a clinical trial.