Inclusion Criteria:

• Non-smoking for at least 6 months;
• Healthy (no medical, psychiatric or sleep disorders);
• No clinically significant deviations from normal in medical history, vital signs, physical examination, blood chemistry and hematology, and ECG;
• Women of childbearing potential must agree to use an acceptable method of birth control, and must have a negative serum pregnancy test;
• Body mass index of > 18 or < 30 kg/m2;
• No drugs or medication likely to affect sleep or alertness, as determined by the investigators;

Exclusion Criteria:

• History of alcohol or substance abuse;
• Positive result on drugs of abuse screening;
• Current or past history of sleep disorders, including but not limited to obstructive sleep apnea, or any significant sleep complaint;
• Psychiatric disorder, including a history of depression or dysthymia (characterized by depressed mood on the majority of days for at least two years);
• Recent acute or chronic medical disorder, including but not limited to hepatic impairment and severe chronic obstructive pulmonary disease;
• History of intolerance or hypersensitivity to melatonin or melatonin agonists;
• Pregnancy or lactation;
• Shift work in the last 3 years;
• Transmeridian travel (2 or more time zones) in past 3 months;
• Any other scientific or medical reason, as determined by the PI, such as non-compliance with protocol or intolerance to inpatient study conditions.