Nineteen studies were included for review (n=425,140): 13 cross-sectional studies (n=275,105), four cohort studies (n=147,433) and two case-control studies (n=2,602).
Risk of Asthma: Acetaminophen significantly increased risk of asthma compared to non-use in adults and children combined (OR 1.63, 95% CI 1.46 to 1.77; nine studies, n=307,842), children who had used acetaminophen in the previous year (OR 1.60, 95% CI 1.48 to 1.74; three studies, n=unclear), children in the first year of life (OR 1.47, 95% CI 1.36 to 1.56; three studies, n=unclear) and adults (OR 1.74, 95% CI 1.36 to 2.28; six studies, n=unclear). Prenatal acetaminophen use significantly increased risk of asthma in children (OR 1.28, 95% CI 1.13 to 1.39; four studies, n=unclear). There was no evidence of significant statistical heterogeneity for these outcomes.
Wheezing: Risk of wheezing was significantly increased in children who used acetaminophen themselves in the previous year (OR 1.97, 95% CI 1.51 to 2.56; six studies, n=unclear) or in the first year of life (OR 1.51, 95% CI 1.24 to 1.83; three studies, n=unclear) and in children whose mothers had used acetaminophen when the child was in utero (OR 1.50, 95% CI 1.10 to 2.05; five studies, n=unclear). There was evidence of significant statistical heterogeneity for these outcomes.
The Egger test did not show publication bias for the outcomes of asthma in adults and wheezing in children. The metaregression analysis did not find a significant effect of study quality on heterogeneity.