The paper presents the first analytically documented Polish case of suicidal poisoning with lamotrigine – a modern antiepileptic and mood stabilizer the mechanism of action of which is not yet fully known, although its chemical structure is similar to that of phenytoin. The authors examine the data available from the forensic and medical files and toxicological examination of the material conducted at the Department of Forensic Medicine and Forensic Toxicology of the Medical University of Silesia in Katowice. Additionally, the paper discusses the possible mechanisms of action and the most important interactions between lamotrigine and other drugs. The case discussed confirms that lamotrigine can be used as a poison with which to commit suicide, particularly by mentally ill patients who have may have easy access to the drug. The LC-MS method allows for the identification and quantitative analysis of lamotrigine in the post mortem biological material.