Safety and Efficacy Study of TNX-201 Capsules for Treatment of Single Tension-Type Headache

The study will be conducted in 4 periods (the Screening Period, the Run-In Period, the Double-Blind Treatment Period and the Follow-up Period) and 4 visits (the Screening Visit, Enrollment Visit, Randomization Visit and End-of-Study Visit). Screening Period- Eligible subjects who provide written informed consent to participate will have study assessments performed at the Screening. Run-In Period- The Run-In Period will last for at least 28 days. During the Run-In period, subjects will be assessed for frequency of headache, study compliance and to ensure they meet all required study criteria for randomization. Double-Blind Treatment Period- The Double-Blind Treatment Period (Treatment Period) will last up to 4 weeks or until a qualifying headache episode has occurred and been treated using the study drug, whichever occurs first. Follow-up Period- All subjects will return to the investigational site for this visit, regardless of whether they have treated a qualifying TTH with study medication. Subjects who have not treated a qualifying TTH with study drug during the Treatment Period will be asked to return study materials and undergo safety evaluations at the End-of-Study Visit and will be discharged from the study. Subjects who have treated a qualifying TTH with study drug during the Treatment Period will ingest a 140 mg dose of open-label TNX-201 at this visit and undergo urine and blood sample collection for 3 hours post-dose to characterize each subject's genetic metabolism and PK profile.