This document discusses therapeutic drug monitoring of lithium, which is used to treat acute mania and bipolar disorder. It outlines the optimal plasma concentration ranges for treatment of mania and prophylaxis, as well as toxic concentration ranges that can cause side effects like renal impairment. TDM is essential for lithium due to its narrow therapeutic index and many drug and disease interactions that influence lithium concentrations. Proper sampling time and monitoring of both lithium levels and clinical response are important for safe and effective treatment.