From Harvard law professor Jeannie Suk Gersen, in the New Yorker:
Because trigger warnings involve assumptions about emotional reactions, particularly with respect to P.T.S.D., psychology researchers have begun to study whether trigger warnings are in fact beneficial. The results of around a dozen psychological studies, published between 2018 and 2021, are remarkably consistent, and they differ from conventional wisdom: they find that trigger warnings do not seem to lessen negative reactions to disturbing material in students, trauma survivors, or those diagnosed with P.T.S.D.
Indeed, some studies suggest that the opposite may be true. The first one, conducted at Harvard by Benjamin Bellet, a Ph.D. candidate, Payton Jones, who completed his Ph.D. in 2021, and Richard McNally, a psychology professor and the author of “IFTTT