In the exploratory multi-center Phase 2 a study safety, tolerability, pharmacodynamics and pharmacokinetics of the Nitric Oxide Synthase inhibitor VAS203 is assessed in patients with moderate and severe traumatic brain injury. Traumatic brain injury patients (32 males) receive 15, 20 and 30 mg/kg VAS203, respectively, by continuous infusion in three cohorts (Cohort 1 open; Cohorts 2 and 3 double blind, randomised placebo-controlled). End of Study for all patients will be Day 14; adverse events and concomitant medications will be documented throughout the study.