The Guidelines in Emergency Medicine Network (GEMNet) has been created to promote best medical practice in a range of conditions presenting to emergency departments (EDs) in the UK. This guideline presents a summary of the best available evidence to guide the management of adult patients who present to the ED following an overdose of tricyclic antidepressant agents (TCA). The document has been developed following discussion among emergency physicians to decide which topics would benefit from the development of clinical guidelines. The document is intended as a guideline for use in the ED by emergency physicians and is based on the review of the best existing evidence for the diagnostic tools and treatments used in this setting. The document is summarised as a clinical decision support guideline that has been presented as an easy to follow algorithm. The intention is for each guideline to be updated and reviewed as further evidence becomes available. The formal revision date has been set at 5 years from publication, although the guideline is subject to continuous informal review.