According to an editorial, these findings should not be considered definitive; noting that although observational studies can provide information on uncommon adverse events in real-world clinical practice that are challenging to assess in randomised trials performed over brief periods, even sophisticated approaches, such as the ones used in this study to address possible biases, do not have the advantages of randomized trials in excluding confounding factors. Therefore the study cannot establish causality and a previous report involving 20,568 patients did not support a causal role of methylphenidate in psychosis. It adds that despite uncertainties regarding causal mechanisms, this study provides important data on the incidence of psychosis observed in routine practice among patients with ADHD, which could inform decision making among patients, families, and physicians when stimulants are prescribed for ADHD, and a balance is desirable between the safety and the effectiveness of a drug for ADHD core symptoms.