Background: Children with obesity are more prone to suffer from psychiatric disorders. However, drug dosing in complex, as most psychotropic agents even in low dosage associated with drug-induced weight gain.

Objectives: To describe the extent of off-label use, polypharmacy and potential adverse drug event (ADE) related to psychotropic drugs in children and adolescence with obesity.

Methods: A retrospective cohort study including 1.593 patient records of children admitted to a Children´s Obesity Clinic, receiving at least one psychotropic drug during an eight-year study period. Off label status and potential ADEs were registered by assessing patient records and medical charts.

Results: One hundred-fifty-eight children received at least one psychotropic drug during the study period and 52% received more than one psychotropic drug concurrently. Both antidepressants and antipsychotics were prescribed significantly more to girls > 12 years than boys (p = 0.02). In total, 61% of the children had at least 1 ADE registered, with significantly increased ADEs when treated with more than one psychotropic drug (p < 0.001). Abnormal weight gain was the most frequently ADE in antipsychotics, affecting 35% of the treated patients. Ninety-one percent had at least one off-label prescription, e.g. non-approved indication (31.5%), age (1.9%), dose (23.8%), and duration of treatment (0.6%).

Conclusion: Off-label use and polypharmacy is frequent among children with obesity treated for psychiatric disorders. It is problematic, since most antipsychotic and antidepressant drugs have metabolic adverse effects. These findings highlight the importance of including this patient population in clinical trials to determine appropriate efficacy-safety relationships.