Antidepressants of the SSRI or SNRI type are the first-line medications used for PTSD and are moderately beneficial for about half of people. Benefits from medication are less than those seen with counselling. It is not known whether using medications and counselling together has greater benefit than either method separately. Medications, other than some SSRIs or SNRIs, do not have enough evidence to support their use and, in the case of benzodiazepines, may worsen outcomes.In the United States, about 3.5% of adults have PTSD in a given year, and 9% of people develop it at some point in their life. In much of the rest of the world, rates during a given year are between 0.5% and 1%. Higher rates may occur in regions of armed conflict. It is more common in women than men.Symptoms of trauma-related mental disorders have been documented since at least the time of the ancient Greeks. A few instances of evidence of post-traumatic illness have been argued to exist from the seventeenth and eighteenth centuries, such as the diary of Samuel Pepys, who described intrusive and distressing symptoms following the 1666 Fire of London. During the world wars, the condition was known under various terms, including shell shock, war nerves, neurasthenia and combat neurosis. The term "post-traumatic stress disorder" came into use in the 1970s in large part due to the diagnoses of U.S. military veterans of the Vietnam War.
Diagnosis
PTSD can be difficult to diagnose, because of:

the subjective nature of most of the diagnostic criteria (although this is true for many mental disorders);
the potential for over-reporting, e.g., while seeking disability benefits, or when PTSD could be a mitigating factor at criminal sentencing
the potential for under-reporting, e.g., stigma, pride, fear that a PTSD diagnosis might preclude certain employment opportunities;
symptom overlap with other mental disorders such as obsessive compulsive disorder and generalized anxiety disorder;
association with other mental disorders such as major depressive disorder and generalized anxiety disorder;
substance use disorders, which often produce some of the same signs and symptoms as PTSD; and
substance use disorders can increase vulnerability to PTSD or exacerbate PTSD symptoms or both; and
PTSD increases the risk for developing substance use disorders. the differential expression of symptoms culturally (specifically with respect to avoidance and numbing symptoms, distressing dreams, and somatic symptoms)

Screening
There are a number of PTSD screening instruments for adults, such as the PTSD Checklist for DSM-5 (PCL-5) and the Primary Care PTSD Screen for DSM-5 (PC-PTSD-5).There are also several screening and assessment instruments for use with children and adolescents. These include the Child PTSD Symptom Scale (CPSS), Child Trauma Screening Questionnaire, and UCLA Post-traumatic Stress Disorder Reaction Index for DSM-IV.In addition, there are also screening and assessment instruments for caregivers of very young children (six years of age and younger). These include the Young Child PTSD Screen, the Young Child PTSD Checklist, and the Diagnostic Infant and Preschool Assessment. Assessment
Evidence-based assessment principles, including a multimethod assessment approach, form the foundation of PTSD assessment.