NAC for Head Trauma-induced Anosmia

Inclusion Criteria: * Admitted to Ryder Trauma Center for observation acutely following head injury (i.e. concussion), with documented hyposmia or anosmia by University of Pennsylvania Smell Identification Test (SIT). * Male or female, aged 18 years or older * Provision of signed and dated informed consent form * Stated willingness to comply with all study procedures and availability for the duration of the study * Ability to take oral medication and be willing to adhere to the NAC regimen * For females of reproductive potential: use of highly effective contraception for at least 1 month prior to screening and agreement to use such a method during study participation and for an additional 4 weeks after the end of NAC administration Exclusion Criteria: * Severe trauma requiring ongoing inpatient treatment beyond 48 hours * Pregnancy (based on urine screening) or lactation * Known allergic reactions to components of NAC, such as Mucomyst * Currently taking nitrates such as nitroglycerine and/or isosorbide regularly * Currently taking azathioprine (Imuran) or cyclophosphamide (Cytoxan) * Known diagnosis of cystinuria (renal condition in which cysteine supplement should be avoided) * Febrile illness within 1 week * Treatment with another investigational drug or other intervention within 3 months * Active sinonasal disease by imaging and/or nasal exam, i.e. rhinosinusitis, nasal polyps * Adults unable to consent * Prisoners, employees or subordinates * Individuals who are not yet adults (infants, children, teenagers). This population is excluded because efficacy has not yet been established in adults.