A Placebo Controlled Trial Of L-Tryptophan In Post-Operative Delirium

Inclusion Criteria: * Included subjects will be 60 years and older undergoing an operation with a planned ICU admission post-operatively. Exclusion Criteria: * Medications that, when combined with tryptophan, increase the risk of serotonin syndrome. The classes of medications include: * monoamine oxidase inhibitors * selective serotonin reuptake inhibitors * serotonin-norepinephrine reuptake inhibitors * triptans * opioids * central nervous system stimulants * bupropion * St. John's Wort * Patients who undergo an operation on their brain. * Factors which prevent delirium assessment with the CAM-ICU: vision impairment or non-fluent English speakers. * A lowered seizure threshold including: * history of seizure disorder * alcohol abuse defined by a high AUDIT score (\>8 females and \>13 males) * benzodiazepine or barbiturate abuse within three months of the study * OR a positive urine toxicology screen for alcohol, benzodiazepines or barbiturates. * Significant liver disease (Child's class B or greater) or significant renal disease (Creatinine ≥2.0). * History of Huntington's or Addison's disease. (As requested by the FDA) * History of bipolar disorder or a psychotic disorder (such as a psychotic major depression, schizophrenia, schizoaffective disorder, or psychosis in Alzheimer's disease or other dementia). (As requested by the FDA) * Women who are not post-menopausal. (As requested by the FDA)