Methoxetamine (MXE) is a ketamine analogue with a high affinity for the N-methyl-D-aspartate (NMDA) receptor. MXE is a newly emerging designer drug of abuse and is widely available through on-line sources and is not detected by routine urine drug screens. In this report, we describe a United States (US) veteran with posttraumatic stress disorder (PTSD) and heavy polysubstance use, who injected high dose MXE for its calming effect. Given MXE's structural similarities to ketamine and recent work showing that ketamine reduces PTSD symptoms, we hypothesize that MXE alleviated this veteran's PTSD symptoms through action at the NMDA receptor and via influences on brain-derived neurotrophic factor (BDNF). To our knowledge, this is the first case report of self-reported use of MXE in the US veteran population. More awareness of designer drugs, such as MXE, is an important first step in engaging patients in the treatment of designer drug addiction in both military/veteran settings and civilian settings.