Changes in the Use of Montelukast for Asthma After a US Food and Drug Administration Boxed Warning

After the FDA added a boxed warning to montelukast, a widely used asthma drug, over potential neuropsychiatric adverse effects in March 2020, incident prescriptions fell nearly 30% and prevalent use declined across all age groups, with the steepest drop among children. These findings indicate that boxed warnings can meaningfully shift prescribing even when causal evidence is mixed and should be carefully tailored to the strength of available data.