Rationale: Advances in sleep research have introduced medications like lemborexant, a dual orexin receptor antagonist. While effective for regulating sleep, overdoses are a concern, especially in suicide attempts. However, limited data exist on lemborexant overdose, prompting this case report to elucidate its clinical course. Patient’s Concern: A 91-year-old Japanese woman with multiple comorbidities, including insomnia and chronic kidney disease, was admitted after ingesting 315 mg of lemborexant in a suicide attempt. Diagnosis: Lemborexant overdose. Interventions: Supportive care with 500 mL of Ringer’s acetate solution at the emergency room. Outcomes: She gradually regained full consciousness with no residual deficits. Due to persistent suicidal ideation, she was transferred to a psychiatric hospital after seven days of supportive care. Lessons: A review of four lemborexant overdose cases managed at our hospital revealed that overdoses primarily induce altered consciousness and are unlikely to cause organ dysfunction. Supportive care is generally sufficient for management. However, given the limited data, further case accumulation is needed to enhance clinical understanding.