This column is the second of a 3-part series describing cases where general medical knowledge, including psychiatric and clinical pharmacology, were instrumental in determining dereliction and direct cause in a malpractice suit. This case summarizes how lamotrigine can cause dangerous consequences if its pharmacology is not properly understood. The case also illustrates how the 4 Ds of a forensic malpractice suit were met in this case. First, there was duty on the part of the prescriber which, if followed, would have prevented or minimized the damages experienced by the patient. Dereliction in the performance of a patient-physician treatment contract was a direct cause of the development of Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) in this patient. An immune-mediated reaction to lamotrigine or one of its metabolites has been extensively reported in the literature, with the risk of this reaction increasing at higher doses and with more rapid titration, fulfilling the elements of direct cause. Dereliction implies a deviation from the standard of care. On the basis of the clinical information from the package insert, more likely than not a deviation from the standard of care occurred in this case when lamotrigine was titrated faster than recommended by the package insert.