Aims: To analyse the clinical features of trimipramine poisoning, identify a minimal toxic dose, and the dose bearing a 50% risk of developing a moderate, severe or fatal outcome. Methods: All acute adult trimipramine monointoxications reported by physicians to the Swiss Toxicological Information Centre between January 1992 and December 2009 were identified. Results: 230 cases (26 confirmed and 204 probable) were analysed; the mean age was 35.7 years, 74% were females. 137 patients showed mild, 54 moderate, and 21 severe symptoms. 3 cases were fatal due to refractory cardiovascular collapse. 93% of the events were attempted or completed suicides. The most common symptoms were central nervous system depression (79.2%), tachycardia (19.1%), and QTc prolongation (13.9%). The severity of poisoning depended significantly on the ingested dose (p<0.001). The minimal dose for moderate symptoms was 250 mg (median dose 1.2 g) and 850 mg for severe symptoms (median dose 2.7 g). The dose for a 50% risk of developing a moderate, severe or fatal outcome was 5.11 g. In 38 patients early gastrointestinal decontamination was performed. Overall, these patients ingested higher trimipramine doses than the late- or not-decontaminated patients (p = 0.113). The median doses were also higher in the decontaminated group within each severity-category except in the fatal cases. Conclusions: We demonstrated that moderate trimipramine poisonings can already occur after ingestion of doses in the high therapeutic range. Poisoned patients have to be monitored for central nervous system depression, dysrhythmias, and QTc prolongation. Early decontamination might be beneficial. © 2012 The Authors. British Journal of Clinical Pharmacology © 2012 The British Pharmacological Society.