Clinical trials at reduced carbon footprint


Two international, randomised control clinical trials, CRASH-1 and CRASH-2, were of similar design, but greater effort was made to reduce the carbon footprint in CRASH-2. CRASH-1 evaluated corticosteroid administration on patient outcomes after traumatic brain injury, while CRASH-2 examined the effect of tranexamic acid administration in bleeding trauma patients. A carbon audit on both trials over one year found that CRASH-1 emitted 92 kg of CO2 per patient while CRASH-2 emitted 25 kg of CO2 per patient. Faster patient recruitment, lighter trial materials and web-based data entry in CRASH-2 accounted for increased carbon efficiency compared to CRASH-1.

Intervention overview

The CRASH-1 (from April 1999 to May 2004), and CRASH-2 (from May 2005 to February 2010) were two clinical trials that evaluated the effects of corticosteroid administration on patient outcomes after traumatic brain injury and the tranexamic acid administration in bleeding trauma patients, respectively. The two trials were of similar design, however, CRASH-1 recruited 10,008 patients, while CRASH-2 recruited double the number, 20,211 patients. Great effort was made to reduce the carbon footprint of the CRASH-2 trial using the strategies outlined in the National Institute for Health and Care Research (NIHR) carbon reduction guidelines.

A carbon audit was conducted for both trials over one year to compare them. Trial related activities that were assessed included coordination centre (electricity, natural gas, steam, heating oil, water, and waste); travel (train, flights, accommodation); commuting (train, bus, underground); and freight delivery (air freight and diesel van).


The total emissions during the evaluation period were 181.3 tonnes CO2eq for CRASH-1 and 108.2 for CRASH-2, which equated to total emissions of 924.6 and 508.5 tonnes CO2eq (assuming that the audit year is representative), respectively. This equated to 25 kg and approximately 7 kg of carbon dioxide per randomised patient (73% less), respectively.

These two clinical trials were conducted for the advancement of medical practice and patient outcomes. It is important to consider ways by which health-related activities, such as health research and clinical trials, that are crucial for the improvement of society, can be conducted at a reduced carbon footprint with minimal impacts on the environment.

Feasibility and potential impact of scale-up

The study helped improve understanding of the activities that contributed to the observed higher or lower carbon emissions in each trial. The study showed that the main determinant of the environmental impact of a clinical trial is patient recruitment. Although CRASH-2 recruited double the number of patients as CRASH-1, patient recruitment was done in a shortened time (4.7 years for CRASH-2, compared with 5.1 years for the CRASH-1). The shorter duration of patient recruitment was attributed mainly to strong clinician interest in the research question, the use of an established network of international collaborators, and the use of a simple trial design with data collection limited to key clinically relevant endpoints. 

Freight delivery of trial medicines was also a major contributing factor to the observed differences.

Finally, differences in the number of office staff also accounted for differences in carbon emissions between the two trials. In CRASH-1, handwritten data received by fax were entered by two staff members at the coordination centre, while direct data entry was used for CRASH-2, reducing the number of staff needed. Teleconferencing and web-based resources further reduced the amount of travel by staff between centres. Particularly in the wake of COVID-19, there are now effective and convenient ways to exchange data and resources, and carry out a wide range of activities and tasks over teleconferencing, which should make this change in how trials are conducted possible.

Additionally, the study provided a deeper understanding of the wider context that may have been a barrier to realising larger effects in CRASH-2. The rapid patient recruitment undertaken for CRASH-2 mainly occurred in Asia, South America, and Africa. In the UK, however, a rapid recruitment was not possible due to regulatory and governance frameworks for clinical trials, potentially limiting their efficiency.


Academic profile / relevant organisation’s page

  • Subaiya, S., Hogg, E., & Roberts, I. (2011). Reducing the environmental impact of trials: a comparison of the carbon footprint of the CRASH-1 and CRASH-2 clinical trials. Trials, 12(1), 1-5.


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