Efficacy and Safety Study of Adipiplon, Placebo and an Active Control in Primary Insomniacs

Inclusion Criteria: * Be between the ages of 21 and 64 years, inclusive; * Have a body mass index (BMI) between 21 and 34 kg/m2, inclusive; * Be a primary insomniac as defined by DSM-IV criteria; in particular difficulty with both sleep initiation and sleep maintenance; * Have subjective Latency to Sleep Onset \> 45 minutes; * Have a mean habitual subjective TST of \<6.5 hours; * Have a TST of 240 - 420 minutes at each of two baseline PSGs; * Have a mean LPS \> 20min, with neither value \<15 minutes and mean WASO \> 40 minutes on baseline PSGs; * Be in good general health as determined by a thorough medical history and physical examination (including vital signs), 12-lead ECG and clinical laboratory tests; * Have clinical laboratory values within normal reference range or not clinically significantly abnormal as judged by the Principal Investigator; * Be off any investigational drug for at least 30 days prior to screening; * If the patient is a female of childbearing potential, she must be using an acceptable method of contraception, must have a negative serum pregnancy test at screening, and must have a negative urine pregnancy test before randomization. * Female patients who have been surgically sterilized or have had a hysterectomy are eligible if they have a negative pregnancy test at screening; * Be able to read, understand, and provide written/dated informed consent before enrolling in the study, and must be willing to comply with all study procedures. Exclusion Criteria: * Clinically significant unstable medical illness; * Evidence or history of clinically significant allergic (except for untreated, asymptomatic, seasonal allergies at time of dosing), hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, or neurological disease; * History of cancer other than basal cell carcinoma, squamous cell carcinoma of the skin or cancer in situ within 5 years of screening; * Supine or sitting blood pressure \> 140/90 mmHg at the screening or baseline visits; * Heart rate \>100 bpm at the screening or baseline visits; * Within the past three years, clinically significant psychiatric illness, including chronic psychiatric illness or any Axis I condition; * History or presence of chronic pain; * History of epilepsy or serious head injury; * Other than primary insomnia, a history of clinically significant sleep disorder including narcolepsy, parasomnia as an adult, circadian rhythm disorder, restless leg syndrome, or on the initial baseline PSG, sleep apnea \[Apnea Hypopnea Index (AHI) \>10\] or Periodic Limb Movement Disorder \[Periodic Limb Movement Arousal Index (PLMAI) \> 10\]; * Any condition that may affect drug absorption; * Smokers who habitually smoke more than 10 cigarettes per day or smoke during the overnight hours; * Travel across more than three time zones, an expected change in sleep schedules of 3 hours or more, or involvement in rotating shift work within 14 days prior to screening or during the study period; * Self-report of napping ≥30 minutes more than 2 times per week within the last month; * Any clinically significant abnormal finding on physical examination, vital signs, ECG, or clinical laboratory tests, as determined by the investigator. (The QTc interval must be ≤430 msec. for males and ≤450 msec for females); * Known or suspected diagnosis of Acquired Immune Deficiency Syndrome, or previous or current positive result on human immunodeficiency virus antibody or antigen testing; * History or laboratory finding of positive hepatitis B surface antigen or hepatitis C core antibody; * History of allergies, or known sensitivity, hypersensitivity, or adverse reaction to any drug similar to adipiplon, including benzodiazepines, or zolpidem, zaleplon, zopiclone, or eszopiclone; * Use of any psychotropic medications, including over-the-counter (OTC) and herbal products, that may affect sleep/wake function within one week or five half-lives (whichever is longer) prior to screening or need to use any of these medications at any time during the study; * Pregnant or lactating females; * Positive serum pregnancy test at screening or urine pregnancy test at baseline; * Recent history (≤ one year) of alcohol or drug abuse, or current evidence of substance dependence or abuse as defined by DSM-IV criteria; * Regular consumption of large amounts of xanthine-containing substances (i.e. more than 5 cups of coffee or equivalent amounts of xanthine-containing substances per day); * Have eaten grapefruit or had grapefruit juice from baseline through the completion of study dosing; * Self report of a usual consumption of more than 14 units of alcohol per week; * Requiring the concomitant usage of any 3A4 inhibitors; * Any prior exposure to adipiplon (formerly known as NG2-73).