IntroductionThe use of pressurised metered-dose inhalers (pMDIs) and asthma exacerbations necessitating healthcare reviews contribute substantially to the global carbon footprint of healthcare. It is possible that a reduction in carbon footprint could be achieved by switching patients with mild asthma from salbutamol pMDI reliever therapy to inhaled corticosteroid-formoterol dry powder inhaler (DPI) reliever therapy, as recommended by the Global Initiative for Asthma (GINA).MethodsThis post hoc analysis included all 668 adult participants in the Novel START trial, who were randomised 1:1:1 to treatment with: as-needed budesonide-formoterol DPI, as-needed salbutamol pMDI, or maintenance budesonide DPI plus as-needed salbutamol pMDI. The primary outcome was carbon footprint of asthma management, expressed as kilograms of carbon dioxide equivalent emissions (kgCO₂e), per person year. Secondary outcomes explored the effect of baseline symptom control and adherence (maintenance budesonide DPI arm only) on carbon footprint.ResultsAs-needed budesonide-formoterol DPI was associated with 95.8% and 93.6% lower carbon footprint compared with as-needed salbutamol pMDI (least squares mean 1.1versus26.2 kgCO₂e; difference −25.0, 95% CI −29.7 to −20.4; p<0.001) and maintenance budesonide DPI plus as-needed salbutamol pMDI (least squares mean 1.1versus17.3 kgCO₂e; difference −16.2, 95% CI −20.9 to −11.6; p<0.001), respectively. There was no statistically significant evidence that treatment differences in carbon footprint depended on baseline symptom control or adherence in the maintenance budesonide DPI arm.ConclusionsThe as-needed budesonide-formoterol DPI treatment option was associated with a markedly lower carbon footprint than as-needed salbutamol pMDI and maintenance budesonide DPI plus as-needed salbutamol pMDI.