This article presents clinically relevant drug interactions which may confront the geriatric psychiatrist. Changes in drug metabolism due to aging, higher medical comorbidity, and frequent polypharmacy all place the older patient at a greater risk of developing a drug-drug interaction. Clinicians must be aware of the potential for such interactions, but they should also be able to determine which of those possible interactions is appropriate for a particular patient. Drug interactions are included in this article based on frequency of the interaction, clinical severity, and frequency of contact with the drugs prescribed by the practicing clinician.