Quetiapine to Reduce Post Concussive Syndrome After Mild Traumatic Brain Injury (mTBI)

Inclusion Criteria: 1. Male or female veterans seeking treatment for mTBI, aged 18-65 years 2. Meet mTBI diagnosis and have PCS symptoms reported on the Neurobehavioral Symptom Inventory (NSI). Six months or more must elapse between the injury and Screening. mTBI diagnosis will be determined using the provisional diagnostic convention recommended by the VA/DoD requiring loss of consciousness, or a period of altered consciousness, or posttraumatic amnesia; 3. Be stable (i.e., no dose changes for \> 1 month) on at least three CNS active psychotropic medications prescribed for symptom relief or psychiatric treatment. 4. Have posttraumatic symptoms measured by PTSD Checklist for DSM-5 (PCL-5) score ≥25. Exclusion Criteria: 1. Moderate or severe TBI, or major neurocognitive disorder (dementia). 2. Meet DSM-5 criteria for schizophrenia, bipolar disorder, schizoaffective disorder, or requiring inpatient hospitalization currently or within past 6 months. 3. Currently taking any antipsychotics or prohibited medication within the past month . 4. Known intolerance to quetiapine or a history of clinically unstable heart, lung, liver, renal, hematological, or endocrinological condition, diabetes mellitus, severe sleep apnea and/or seizure disorder. 5. Substance use disorder severe enough to require medication treatment or medical detoxification or inpatient hospitalization within 6 months of screening. 6. Reporting suicidal ideation of type 4 or 5 in the Columbia Suicide Severity Rating Scale (CSSRS) in the past 3 months prior to screening or at screening or baseline visit (i.e. active suicidal thought with method and intent but without specific plan, or active suicidal thought with method, intent, and plan); or homicidal ideation with intent or plan to harm others within 90 days or suicide attempt; or suicidal behavior within 6 months prior to screening. (Note: Study psychiatrist will be immediately notified when SI or HI intent is positive) 7. Current or known history of cardiac arrhythmia or QTc interval ≥ 470 milliseconds. 8. Pregnant or lactating women and those of child-bearing potential not using a reliable method of contraception will be excluded from participating in the study.