“Background: The prevention of long‐term psychological distress following traumatic events is a major concern. Systematic reviews have suggested that individual psychological debriefing is not an effective intervention at preventing post‐traumatic stress disorder (PTSD). Over the past 20 years, other forms of intervention have been developed with the aim of preventing PTSD.

Objectives: To examine the efficacy of psychological interventions aimed at preventing PTSD in individuals exposed to a traumatic event but not identified as experiencing any specific psychological difficulties, in comparison with control conditions (e.g. usual care, waiting list and no treatment) and other psychological interventions.

Search methods: We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, PsycINFO and ProQuest’s Published International Literature On Traumatic Stress (PILOTS) database to 3 March 2018. An earlier search of CENTRAL and the Ovid databases was conducted via the Cochrane Common Mental Disorders Controlled Trial Register (CCMD‐CTR) (all years to May 2016). We handsearched reference lists of relevant guidelines, systematic reviews and included study reports. Identified studies were shared with key experts in the field.

We conducted an update search (15 March 2019) and placed any new trials in the ‘awaiting classification’ section. These will be incorporated into the next version of this review, as appropriate.

Selection criteria: We searched for randomised controlled trials of any multiple session (two or more sessions) early psychological intervention or treatment designed to prevent symptoms of PTSD. We excluded single session individual/group psychological interventions. Comparator interventions included waiting list/usual care and active control condition. We included studies of adults who experienced a traumatic event which met the criterion A1 according to the Diagnostic and Statistical Manual (DSM‐IV) for PTSD.

Main results: This is an update of a previous review.

We included 27 studies with 3963 participants. The meta‐analysis included 21 studies of 2721 participants. Seventeen studies compared multiple session early psychological intervention versus treatment as usual and four studies compared a multiple session early psychological intervention with active control condition.

Low‐certainty evidence indicated that multiple session early psychological interventions may be more effective than usual care in reducing PTSD diagnosis at three to six months’ follow‐up (RR 0.62, 95% CI 0.41 to 0.93; I² = 34%; studies = 5; participants = 758). However, there was no statistically significant difference post‐treatment (RR 1.06, 95% CI 0.85 to 1.32; I² = 0%; studies = 5; participants = 556; very low‐certainty evidence) or at seven to 12 months (RR 0.94, 95% CI 0.20 to 4.49; studies = 1; participants = 132; very low‐certainty evidence). Meta‐analysis indicated that there was no statistical difference in dropouts compared with usual care (RR 1.34, 95% CI 0.91 to 1.95; I² = 34%; studies = 11; participants = 1154; low‐certainty evidence) .At the primary endpoint of three to six months, low‐certainty evidence indicated no statistical difference between groups in reducing severity of PTSD (SMD –0.10, 95% CI –0.22 to 0.02; I² = 34%; studies = 15; participants = 1921), depression (SMD –0.04, 95% CI –0.19 to 0.10; I² = 6%; studies = 7; participants = 1009) or anxiety symptoms (SMD –0.05, 95% CI –0.19 to 0.10; I² = 2%; studies = 6; participants = 945).

No studies comparing an intervention and active control reported outcomes for PTSD diagnosis. Low‐certainty evidence showed that interventions may be associated with a higher dropout rate than active control condition (RR 1.61, 95% CI 1.11 to 2.34; studies = 2; participants = 425). At three to six months, low‐certainty evidence indicated no statistical difference between interventions in terms of severity of PTSD symptoms (SMD –0.02, 95% CI –0.31 to 0.26; I² = 43%; studies = 4; participants = 465), depression (SMD 0.04, 95% CI –0.16 to 0.23; I² = 0%; studies = 2; participants = 409), anxiety (SMD 0.00, 95% CI –0.19 to 0.19; I² = 0%; studies = 2; participants = 414) or quality of life (MD –0.03, 95% CI –0.06 to 0.00; studies = 1; participants = 239).

None of the included studies reported on adverse events or use of health‐related resources.

Authors’ conclusions: While the review found some beneficial effects of multiple session early psychological interventions in the prevention of PTSD, the certainty of the evidence was low due to the high risk of bias in the included trials. The clear practice implication of this is that, at present, multiple session interventions aimed at everyone exposed to traumatic events cannot be recommended. There are a number of ongoing studies, demonstrating that this is a fast moving field of research. Future updates of this review will integrate the results of these new studies.”