RecruitingPhase 2Drug trialPrevention/Reduction of ASRs and PTSD to Sustain Civilian Performance With Sublingual Cyclobenzaprine HCl (TNX-102 SL)This study will examine the safety and efficacy of TNX-102 SL to reduce ASR symptoms and behavioral changes among patients presenting to the emergency department (ED) after motor vehicle collision (MVC). Specifically, the investigators will perform the Optimizing Acute Stress reaction Interventions with TNX-102 SL (OASIS) Trial, a double-blind placebo-controlled randomized clinical trial (RCT) to determine if TNX-102 SL initiated in the ED in the hours after MVC to high risk individuals, treats/reduces acute stress reaction (ASR)/acute stress disorder (ASD) symptoms (primary outcome), improves neurocognitive function, and prevents/reduces posttraumatic stress (PTS) symptoms (secondary outcomes) long term. 180 participants will be randomized, receive study drug in ED and be discharged with a 2-week drug supply. Prior to initial dose of study drug administration, and during the hours, days, and weeks after participants will receive serial longitudinal assessments of psychological and somatic symptoms, neurocognitive function, and adverse events.