Thiopental is a barbiturate used in traumatic brain injuries (TBIs) to reduce intracranial pressure (ICP) and to manage cerebral ischemia. As thiopental follows Michaelis-Menten kinetics, therapeutic drug monitoring (TDM) has been used in practice to improve efficacy and reduce adverse effects. However, its role is still debatable, and TDM is not widely practiced. Current evidence suggests that thiopental therapy may improve mortality and functional outcome in a subpopulation of patients with severe TBI with elevated ICP refractory to conventional medical therapy. Several analytical methods are available to quantify thiopental concentrations. This review uses a previously published 9-step decision-making algorithm to determine whether TDM of thiopental in TBI is warranted. There seems to be poor correlation between thiopental concentration and pharmacological response in terms of neurological response, ICP, electroencephalography, and drug toxicity. There is no established therapeutic range for thiopental continuous infusion due to a wide range of plasma concentrations corresponding to efficacy (25-50 mg/L) and toxicity (30-70 mg/L) and the resulting overlap between the 2. Thiopental exhibits intrapatient and interpatient variability due to age, obesity, renal and hepatic dysfunction, Michaelis-Menten kinetics, and hepatic enzyme autoinduction. Available evidence suggests that TDM of thiopental continuous infusion is not beneficial in improving efficacy or avoiding toxicity. There are however 2 possible scenarios in which TDM may provide additional information to sound clinical judgment. The first is providing patient-specific plasma target concentration to guide titration of therapy. The second scenario is differentiating between brain death and barbiturate-induced coma.