Patients with blunt head injury are at high risk of venous thromboembolism. However, pharmacologic thromboprophylaxis (PTP) may cause progression of intracranial hemorrhage, and clinicians must often weigh up the risks and benefits. This review aimed to determine whether adding PTP to mechanical prophylaxis confers net benefit or harm and the optimal timing, dose, and agent for PTP in patients with blunt head injury. METHODS: We searched MEDLINE, EMBASE, The Cochrane Library Central Register of Controlled Trials (CENTRAL), and www.clinicaltrials.gov on April 24, 2013, to identify controlled studies and ongoing trials that assessed the efficacy or safety of thromboprophylaxis interventions in the early management of head-injured patients. Studies were classified based on types of interventions and comparisons, and the quality of included studies was assessed using Cochrane risk-of-bias tool and the Newcastle-Ottawa Quality Assessment Scale. We intended to undertake a meta-analysis if studies were sufficiently similar. RESULTS: Sixteen studies met the inclusion criteria, including four randomized controlled trials. At least two randomized controlled trials were at high risk of bias owing to inadequate randomization and concealment of allocation, and observational studies were potentially confounded by substantial differences between comparison groups. Heterogeneity of included studies precluded meta-analysis. Results were mixed, with some studies supporting and others refuting addition of PTP to mechanical interventions. Little evidence was available about dose or choice of agent. The safety and efficacy of early PTP in patients without early progression of hemorrhage is unclear. CONCLUSION: There is currently insufficient evidence to guide thromboprophylaxis in patients with blunt head injury. Standardized definitions and outcome measurements would facilitate comparison of outcomes across future studies. Studies in mixed populations should report head-injured specific subgroup data. Future randomized controlled trials should investigate the efficacy and safety of early pharmacologic prophylaxis in addition to mechanical intervention.