Understanding sex differences among persons with moderate-to-severe traumatic brain injury (TBI) is critical to addressing the unique needs of both males and females from acute care through to rehabilitation. Epidemiological studies suggest that 7 of every 10 persons with moderate-to-severe TBI are male, with females representing about 30%–33%.

To examine the proportion of female and male individuals included in randomized controlled trials (RCTs) of interventions for moderate-to-severe TBI.

A systematic review was conducted in line with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines up to and including December 2022 using MEDLINE, PubMed, Scopus, CINAHL, EMBASE and PsycINFO databases. Studies were included if they met the following criteria: (1) human participants with a mean age ≥18 years, (2) ≥50% of the sample had moderate-to-severe TBI and (3) the study design was a RCT. Data extracted included author, year, country, sample size, number of female/male participants and time post-injury.

595 RCTs met the criteria for inclusion, published between 1978 and 2022, totaling 86,662 participants. The average proportion of female participants was 23.14%, and the percentage increased a small but significant amount over time. There was a significantly lower percentage of female participants in RCTs initiated in the acute phase (≤ 1 month) when compared with RCTs conducted in the chronic phase (≥ 6 months) post-injury (p < 0.001).

Female participants are underrepresented in RCTs of moderate-to-severe TBI. Addressing this underrepresentation is critical to establish effective treatments for all persons with TBI.