Trigger warnings are not helpful for trauma survivors; it is less clear whether trigger warnings are explicitly harmful

Jones, Payton J., Benjamin W. Bellet, and Richard J. McNally. 2019. “Helping or Harming? The Effect of Trigger Warnings on Individuals with Trauma Histories.” OSF Preprints. July 10. doi:10.31219/osf.io/axn6z

Abstract
Objective: Trigger warnings alert trauma survivors about potentially disturbing forthcoming content. However, most empirical studies on trigger warnings indicate that they are either functionally inert or cause small adverse side effects. These evaluations have been limited to either trauma-naïve participants or mixed samples. Accordingly, we tested whether trigger warnings would be psychologically beneficial in the most relevant population: survivors of serious trauma.
Method: Our experiment was a preregistered replication and extension of a previous one (Bellet, Jones, & McNally, 2018); 451 trauma survivors were randomly assigned to either receive or not receive trigger warnings prior to reading potentially distressing passages from world literature. They provided their emotional reactions to each passage; self-reported anxiety was the primary dependent variable. 
Results: We found no evidence that trigger warnings were helpful for trauma survivors, for those who self-reported a PTSD diagnosis, or for those who qualified for probable PTSD, even when survivors' trauma matched the passages’ content. We found substantial evidence that trigger warnings countertherapeutically reinforce survivors' view of their trauma as central to their identity. Regarding replication hypotheses, the evidence was either ambiguous or substantially favored the hypothesis that trigger warnings have no effect.
Conclusions: Trigger warnings are not helpful for trauma survivors. It is less clear whether trigger warnings are explicitly harmful. However, such knowledge is unnecessary to adjudicate whether to use trigger warnings – because trigger warnings are consistently unhelpful, there is no evidence-based reason to use them.