INTRODUCTION: Behavioral health is essential for the safety, well-being, and performance of crewmembers in both human spaceflight and Antarctic exploration. Over the past five decades, psychiatric issues have been documented in orbital spaceflight. In Antarctica, literature suggests up to 5% of wintering crewmembers could meet criteria for a psychiatric illness, including mood disorders, stressor-related disorders, sleep-wake disorders, and substance-related disorders. Experience from these settings indicates that psychiatric disorders on deep space missions must be anticipated. An important part of planning for the psychological health of crewmembers is the onboard provision of psychotropic drugs. These medications have been available on orbital missions. A greater variety and supply of these drugs exist at Antarctic facilities. The size and diversity of a deep space psychiatric formulary will be greater than that provided on orbital missions. Drugs to be provisioned include anxiolytics, antidepressants, mood stabilizers, antipsychotics, and hypnotics. Each drug category should include different medications, providing diverse pharmacokinetic, pharmacodynamic, and side effect profiles. The formulary itself should be rigorously controlled, given the abuse potential of some medications. In-flight treatment strategies could include psychological monitoring of well-being and early intervention for significant symptoms. Psychiatric emergencies would be treated aggressively with behavioral and pharmacological interventions to de-escalate potentially hazardous situations. On long-duration space missions, a robust psychiatric formulary could provide crewmembers autonomy and flexibility in treating a range of behavioral issues from depression to acute psychosis. This will contribute to the safety, health, and performance of crewmembers, and to mission success.Friedman E, Bui B. A psychiatric formulary for long-duration spaceflight. Aerosp Med Hum Perform. 2017; 88(11):1024–1033.