Evaluation of: Goodacre S, Cohen J, Bradburn Met al.Intravenous or nebulised magnesium sulphate versus standard therapy for severe acute asthma (3Mg trial): a double-blind, randomized controlled trial.Lancet Respir. Med.1, 293–300 (2013). Acute exacerbations of asthma are common. The current recommended treatment approach to managing an acute asthma exacerbation is to administer a short-acting inhaled β2-agonist (SABA). SABAs are rapidly effective but may not provide the bronchodilation needed to restore adequate lung function. Consequently, in severe acute asthma exacerbations, despite a standard approach to treatment including SABAs, hospitalization is common. Magnesium is a bronchodilator that may provide additional benefit to SABAs in managing acute asthma exacerbations. In this article, the comparative effectiveness of inhaled and intravenous magnesium in addition to standard therapy is evaluated in the management of severe acute asthma exacerbations. Although neither inhaled nor intravenous magnesium achieved the protocol-specified benefits, intravenous magnesium was associated with fewer hospitalizations and a trend for greater improvement in the symptom of breathlessness than inhaled magnesium.