Unanticipated Pathological Laughter Following Atomoxetine Administration in a Child With Autism Spectrum Disorder and Attention-Deficit/Hyperactivity Disorder.

Introduction: Atomoxetine, a selective norepinephrine reuptake inhibitor (NRI), is commonly prescribed for attention-deficit/hyperactivity disorder (ADHD) and has shown effectiveness in children with autism spectrum disorder (ASD). Although mood disturbances and psychiatric symptoms are recognized side effects, pathological laughter has not been previously reported.

Case Presentation: We present the case of a 6-year-old boy diagnosed with both ASD and ADHD who developed sudden, uncontrollable episodes of pathological laughter after beginning low-dose atomoxetine (5 mg/day, ~0.25 mg/kg). The child had a history of hyperactivity and aggression, managed with risperidone and clonidine. Within 5 days of initiating atomoxetine, he exhibited frequent, spontaneous laughter lasting 2-5 min without any apparent emotional trigger. These episodes resolved within 10 days despite continued atomoxetine treatment, coinciding with a minor increase in risperidone dosage. Following this period, the child displayed noticeable improvements in attention, eye contact, and overall cooperation. Atomoxetine was later increased to 10 mg/day, with no recurrence of pathological laughter.

Conclusion: This case suggests that pathological laughter may be a rare but temporary side effect of atomoxetine, even at low doses. Given the child's familial history of bipolar disorder and the influence of catecholamines on mood regulation, clinicians should be vigilant in monitoring mood-related side effects in children with neurodevelopmental disorders. This report emphasizes the need for personalized treatment approaches and further investigation into the mechanisms and risk factors underlying this phenomenon.