Psychopharmacologic intervention for elderly patients requires careful considerations for physical characteristics, comorbid medical illness, and interaction between drugs for psychotropic and somatic diseases drugs. Elderly patients often suffer from depression, delirium, and dementia, which occasionally coexist with each other. Antidepressants, antipsychotics, anxiolytics and hypnotics are prescribed according to the targeted psychiatric symptoms.
 Drug effect tends to be strengthened and prolonged pharmacodynamically in elderly patients because of decline of drug clearance in liver and kidney,prolongation of elimination half life of lipophilic drug resulted from reduced muscle tissue,and elevated free serum drug level induced by low albuminemia. Elderly patients pharmacokinetically develop adverse effects in relatively lower serum drug level. Lower initial dose and slow titration should be strongly recommended.
 Cerebrovascular disease and neurodegerative disease are frequently observed among elderly patients. Significant number of patients with cerebrovascular disease are complicated with depression, delirium, and, in lower prevalence, dementia. Although drugs used in acute phase stroke have no pharmacodynamic interaction with psychotropics,many patients receive pharmacotherapy for a wide variety of underlying medical illnesses. Warfarin must be carefully titrated with continuous monitoring of PT-INR during concurrent use of tricyclic antidepressants and selective serotonin reuptake inhibitors.
 Alzheimer’s disease and Parkinson’s disease are highly prevalent and clinically important neurodegerative disease in elderly population. Patients with Alzheimer’s disease frequently exhibit delirium soon after hospitalization,which necessitates appropriate pharmacotherapy with psychotropics. After Food and Drug Foundation warned against antipsychotic use for patients with dementia, this off-label use are considered to be avoided but often selected with the family’s consent in daily clinical practice. Patients with Parkinson’s disease frequently coincide with depression and receive antidepressant treatment. If selegiline is prescribed, antidepressants cannot be initiated without discontinuation of selegiline. When delirium develops in patients with Parkinson’s disease, second generation antipsychotics such as quetiapine are firstly administered with caution for deterioration of motor symptoms.