Prevention/Reduction of ASRs and PTSD to Sustain Civilian Performance With Sublingual Cyclobenzaprine HCl (TNX-102 SL)

Inclusion Criteria: 1. ≥ 18 years and ≤ 55 years of age 2. Presentation to ED within 72 hours of MVC 3. Anticipated to be discharged home from the ED 4. Stated willingness to comply with all study procedures and availability for the duration of the study 5. Consent to receive unencrypted communications 6. Has a smartphone with continuous service for ≥ 1 year 7. Has a personal email address they regularly access 8. Able to speak and read English 9. Pain severity in the ED ≥ 4 (0-10 numeric rating scale) 10. People who are not of childbearing potential (e.g., hysterectomy, bilateral oophorectomy, or confirmed postmenopausal for at least last 12 consecutive months) 11. People with the capacity to conceive a pregnancy must agree to employ a highly effective form of birth control throughout the first 21 days of study participation (e.g., oral, injected, transdermal, or implanted hormonal methods of contraception for at least one full menstrual cycle prior to study drug administration; placement of an intrauterine device (IUD) or intrauterine system (IUS); or double barrier methods such as condoms and diaphragms) Exclusion Criteria: 1. Substantial comorbid injury (e.g., long bone fracture) 2. People of childbearing potential who are pregnant, breastfeeding, planning to become pregnant, or not using a highly effective form of contraception (e.g., implants, intrauterine devices (IUDs), tubal ligation, hormonal birth control pills, patches, vaginal rings, or injections) during their participation 3. Prisoner status 4. Any chronic daily opioid use prior to MVC 5. Active psychosis, suicidal ideation, or homicidal ideation 6. Plans for hospital admission 7. History of arrhythmias, heart block or conduction disturbances, congestive heart failure 8. Currently in the acute recovery phase of myocardial infarction 9. Hypersensitivity to cyclobenzaprine or the excipient in TNX-102 SL or placebo formulations 10. History of urinary retention, angle-closure glaucoma, increased intraocular pressure, or hyperthyroidism (TSH \< lower limit of normal) 11. Concomitant use of monoamine oxidase (MAO) inhibitors or within 14 days after their discontinuation due to risk of potential fatal drug-drug interactions 12. Current or planned use of the following prohibited concomitant medications during study participation: anticholinergic medications, guanethidine, selective serotonin reuptake inhibitors (SSRIs) , serotonin norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), tramadol, bupropion, meperidine, verapamil, MAO inhibitors, anticholinergic medications, guanethidine, potent cytochrome P450 subtype 3A4 inhibitor, St. John's wort, chronic use muscle relaxants or planned use after MCV or other prohibited concomitant medications listed in section 5.6. PI to assess individual cases where single dose of muscle relaxant is prescribed in ED for inclusion 13. Any hepatic impairment or renal disease (defined as AST OR ALT \> 3 times the upper limit of normal) or renal disease (defined as GFR ≤ 80 mL/min) 14. Lacking capacity to provide informed consent (receipt of sedative, hypnotic agent making the patient non-decisional for consent) 15. Any other history or condition that would, in the site investigator's judgement, indicate that the patient would very likely be non-compliant with the study or unsuitable for the study (e.g., might interfere with the study, confound interpretation, or endanger patient) 16. Elevated baseline blood pressure defined as systolic blood pressure ≥ 170 mmHg or diastolic blood pressure ≥ 100 mmHg and or elevated heart rate of ≥115 17. Abnormal baseline ECG as defined as: QRS duration ≥ 120 ms; QTc \> 460 ms; not in sinus rhythm; or 1st, 2nd, or 3rd degree heart block indicated 18. Substance or alcohol use disorder, bipolar disorder, or schizophrenia 19. History of severe or unexplained oral, or oropharyngeal swelling or edema