Lithium is approved for treating bipolar disorder and is dosed based on achieving a target serum level. Common side effects include thyroid dysfunction, diabetes insipidus, tremor, weight gain and cognitive impairment. Dosing must be adjusted for renal impairment and in elderly patients due to reduced clearance. Lithium has a half-life of 14-24 hours and is primarily excreted unchanged in the urine. Monitoring of serum levels and side effects is important during long-term lithium treatment.