Evidence Level B
Randomized controlled trials (RCTs) of <200 participants, methodologically flawed RCTs of >200 participants, methodologically flawed systematic reviews (SRs) or good quality observational (cohort) studies.
Symptom severity: there is medium-quality evidence that adding a long-acting beta2 agonist (LABA) to inhaled corticosteroids is more effective than inhaled corticosteroids alone at reducing the need for systemic corticosteroids in people with poorly controlled asthma and at improving FEV1 and peak expiratory flow rate (PEFR) in people with poorly controlled asthma.
More info from BMJ Clinical Evidence
