Open Label Study to Assess the Absolute Bioavailability of Tasimelteon (HETLIOZ™)

Inclusion Criteria: 1. Men and women ages 18 - 55 years, inclusive; 2. Non-smokers \[abstinence from smoking for at least 6 months before the screening visit\] and test negative for cotinine at screening and baseline; 3. Subjects with Body Mass Index (BMI) of ≥18 and ≤25 kg/m2 (BMI = weight (kg)/ \[height (m)\]2); 4. Males, non-fecund females (i.e., surgically sterilized, if procedure was done 6 months before screening or subject is postmenopausal, without menses for 6 months before screening), or females of child-bearing potential using an acceptable method of birth control for a period of 35 days before the first dosing, and females must have a negative pregnancy test at the screening and baseline visits; Note 1: Acceptable methods of birth control include any one of the following: abstinence, vasectomized sexual partner, hormonal methods (i.e. pill, hormonal IUD, Depo-Provera, implants, patch, intravaginal device \[NuvaRing\]), intrauterine device (IUD \[copper banded coils\]), diaphragm, cervical cap, or condom with spermicidal jelly or foam 5. Vital signs (after 3 minutes resting in a semi-supine position) which are within the ranges shown below: 1. Body temperature between 35.0-37.5 °C; 2. Systolic blood pressure between 90-150 mmHg; 3. Diastolic blood pressure between 50-95 mmHg; 4. Pulse rate between 50-100 bpm. 6. Ability and acceptance to provide written informed consent; 7. Willing and able to comply with study requirements and restrictions; 8. Subjects must be in good health as determined by past medical history, physical examination, electrocardiogram, clinical laboratory tests and urinalysis; Exclusion Criteria: 1. History of recent (within six months) drug or alcohol abuse as defined in DSM-V, Diagnostic Criteria for Drug and Alcohol Abuse or evidence of such abuse as indicated by the laboratory assays conducted during the Screening Visit or at Baseline; 2. Any major surgery within three months of the first Baseline visit or any minor surgery within one month; 3. History or current evidence of cardiovascular, hepatic, hematopoietic, renal, gastrointestinal or metabolic dysfunction or psychiatric disease judged by the Investigator to be clinically significant; 4. Subjects who are currently considered a suicide risk, any subject who has ever made a suicide attempt, or those who are currently demonstrating active (within the past 6 months) suicidal ideation as deemed by the Columbia Suicide Severity Rating Scale (C-SSRS); 5. Any condition requiring the regular use of medication except those listed in Section 8.2; 6. Exposure to any investigational drug, including placebo, within 30 days or 5 half-lives (whichever is longer) of baseline 7. Exposure (within 2 weeks of Day -1) to any over-the-counter medications including melatonin, dietary supplements and/or herbal remedies, except those listed on Section 8.2; 8. Treatment with any drug known to cause major organ system toxicity (e.g., chloramphenicol or tamoxifen) during the 60 days preceding the Screening visit; 9. History of intolerance and/or hypersensitivity to tasimelteon, and/or drugs similar to tasimelteon including melatonin; 10. Donation or loss of 400 mL or more of blood within one month prior to the Baseline Visit; 11. Significant illness within the two weeks prior to Baseline; 12. Pregnant or lactating females; 13. History of porphyria or liver disease and/or positive for one or more of the following serological results: 1. A positive hepatitis C antibody test (anti-HCV) 2. A positive hepatitis B surface antigen (HBsAg) 3. A positive HIV test result 14. Use of any food or beverage containing grapefruit or grapefruit juice, apple or orange juice, vegetables from the mustard green family (e.g. kale, broccoli, watercress, collard greens, kohlrabi, Brussels sprouts, mustard greens) and charbroiled meats for at least 2 weeks before the Baseline Visit until the end of the study; 15. Inability to be venipunctured and/or tolerate venous access; 16. Previous participation in a BMS-214778, VEC-162, or tasimelteon study; 17. Subjects who are unable to read or speak English; 18. Any other sound medical reason as determined by the clinical Investigator.