Safety and Efficacy of Angiotensin (1-7) in Persons With Moderate to Severe Traumatic Brain Injury

The goal of this clinical trial is to test the safety of the drug Angiotensin (1-7) and learn whether it works well as a treatment in people who have suffered a moderate to severe traumatic brain injury (TBI). The main questions this trial aims to answer are: * Is Angiotensin (1-7) safe? * Does Angiotensin (1-7) improve mental functioning and reduce physical signs of brain damage in people who have suffered a moderate to severe TBI? Participants will: * Complete 21 days of study treatment consisting of a once-daily injection. * Provide blood samples. * Undergo two magnetic resonance imaging (MRI) scans of the brain. * Complete specific tasks and questionnaires that allow researchers to evaluate the participant's brain and psychological functioning. Researchers will compare three groups: two groups that receive different doses of Angiotensin (1-7) and one group that receives a look-alike treatment with no active drug. This will allow researchers to see if the drug has any negative effects and whether it improves mental functioning and physical signs of brain damage after a TBI.