Operational stress injury (OSI) is a non-clinical and non-medical term apparently coined by Veterans Affairs Canada [1] yet applicable elsewhere and used to describe a distinct category of occupational stress injury, referring to mental health challenges related to military or police service (the latter reserved in Canada for service in the Royal Canadian Mounted Police (RCMP)) [2]. Occupational stress injuries encompass a broad range of psychological and related conditions resulting from work-related activities that interfere with a person’s professional and personal life, including anxiety, depressive, trauma- and stressor-related, and substance-related disorders ^[3][4][3,4]. Operational stressors that may result in OSI can include service-related events beyond combat, such as service-related accidents in unrelated to combat activities, as well as sexual trauma caused by peers and others involved in one’s service. OSIs do not relate to injuries that are not associated with service. For example, grief from the loss of a loved one outside the service during active service is not typically a cause of OSI, although if it is associated with lack of support by service peers and/or supervisors, that can cause OSI (sometimes termed consequential OSI). Due to the common stress hypersensitivity related to post-traumatic and other OSI-related experiences, people with OSIs often develop anxiety and substance-related disorders, e.g., as learned stress intolerance and as (maladaptive) self-help coping, respectively.

The recognition of operational stress injuries (OSIs) traces back to earlier periods in history, with notable observations of the psychological impact of combat experiences on soldiers dating back to the mid-19th century. During World War I, the notion of shell shock was addressed, highlighting the psychological toll of warfare on military personnel [5]. However, it was later in the 20th century when the term “post-traumatic stress disorder” (PTSD) was coined, reflecting a deeper understanding of the condition and its broader manifestations beyond the context of combat experiences [6]. Key breakthroughs in the late 1990s and early 2000s furthered awareness of mental health issues in the military and law enforcement communities. Research efforts shed light on the prevalence and impact of OSIs, paving the way for proactive support approaches and comprehensive programs focused on OSI prevention, diagnosis, and treatment. While the term OSI is most commonly used and understood in Canadian settings when referring to military or police service, it is also relevant internationally and to other first responder populations. In any cultural context, as long as the injury develops during, as a result of, or is worsened by, military/police service, then it can be considered an OSI.

Despite progress, fully comprehending OSI’s scope and complexity remains a challenge and hence disrupts related care. OSIs encompass various mental disorders as noted above [1]. The lack of a coherent and comprehensive description of OSI in the peer-reviewed literature requires further scholarly work and publication. OSIs are common among military personnel and RCMP members, often co-occurring with physical health challenges [7]. The study of OSIs is important due to their considerably disruptive impact on individuals and their social supports [8], including considerable suffering and dysfunction; as well, it is important to address related resilience and post-traumatic growth [9].

OSI remains a critical issue requiring ongoing research and collaboration to effectively support military personnel, veterans, and RCMP (and other police forces’) members and retirees. Understanding OSI’s history and current status is important for further research and development including in relation to best practices in order to reduce incidence and enhance recovery in relation to OSIs.

This entry aims to provide a comprehensive yet concise overview of OSIs, encompassing diagnosis-specific and transdiagnostic aspects. By examining symptomatology, epidemiology, etiology, treatment, and lived experience, valuable insights will be offered here for all stakeholders, such as mental health care providers, policymakers, and service users.