This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

1) To provide an estimate of the efficacy of medication in preventing the development of post‐traumatic stress disorder following exposure to a traumatic event. The efficacy of medication in reducing symptom severity for those individuals who subsequently develop PTSD will also be considered.

2) To determine whether particular classes of medication are more effective and/or acceptable than others in the prevention of PTSD.

3) To assess whether depression is a predictor of treatment response in the prevention of PTSD.