BackgroundThe Global Initiative for Asthma recommends as-needed inhaled corticosteroid (ICS)-formoterol as an alternative to maintenance ICS plus short-acting β₂-agonist (SABA) reliever at step 2 of its stepwise treatment algorithm. Our aim was to assess the efficacy and safety of these two treatment regimens, with a focus on prevention of severe exacerbation.MethodsWe performed a systematic review and meta-analysis of all randomised controlled trials (RCTs) comparing as-needed ICS-formoterol with maintenance ICS plus SABA. MEDLINE, Embase, the Cochrane Central Register of Controlled Trials and Clinicaltrials.gov were searched from database inception to 12 December 2019. The primary outcome was time to first severe exacerbation. RCTs were excluded if they used as-needed budesonide-formoterol as part of a maintenance and reliever regimen, or did not report on severe exacerbations. The review is registered with PROSPERO (identifier number CRD42020154680).ResultsFour RCTs (n=8065 participants) were included in the analysis. As-needed ICS-formoterol was associated with a prolonged time to first severe exacerbation (hazard ratio 0.85, 95% CI 0.73–1.00; p=0.048) and reduced daily ICS dose (mean difference −177.3 μg, 95% CI −182.2–−172.4 μg). Asthma symptom control was worse in the as-needed group (Asthma Control Questionnaire-5 mean difference 0.12, 95% CI 0.09–0.14), although this did not meet the minimal clinically important difference of 0.50 units. There was no significant difference in serious adverse events (OR 1.07, 95% CI 0.84–1.36).ConclusionAs-needed ICS-formoterol offers a therapeutic alternative to maintenance low-dose ICS plus SABA in asthma and may be the preferred option when prevention of severe exacerbation is the primary aim of treatment.