Abstract Background The effects of restrictive versus liberal transfusion strategies in critically ill patients with traumatic brain injury (TBI) and anemia, particularly in adult patients with moderate to severe TBI, remain inconclusive. Therefore, this systematic review and meta-analysis aim to evaluate the comparative impact of restrictive and liberal red blood cell transfusion strategies among critically ill adult patients with moderate to severe TBI. Methods We conducted a search of PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials from their inception through October 20, 2024, to identify randomized controlled trials that compared restrictive (transfusions at a hemoglobin level of ≤ 7 g/dL) and liberal (transfusions at a hemoglobin level of ≤ 9–10 g/dL) transfusion strategies in adult patients with TBI. The primary outcome was mortality, with secondary outcomes including an unfavorable neurological outcome at six months, as determined by the Glasgow Outcome Scale (GOS