The purpose of this study is to test the effects of eszopiclone on daytime sleep and overnight wakefulness in shift workers.

The current study seeks to extend the currently available treatments for SWSD by addressing the putative root cause of the problem-the inability of night-shift workers with or without SWSD- to obtain adequate daytime sleep in the face of the circadian drive for alertness that increases across the biological day. Even healthy, young subjects who are sleep-deprived overnight exhibit daytime sleep marked by frequent awakenings and low sleep efficiency, less slow-wave sleep, and altered sleep architecture, e.g. earlier predominance of REM sleep. Many night-workers routinely report 3-6 hours of habitual sleep duration for daytime sleep. Pharmacological interventions to decrease awakenings and improve total sleep time during daytime sleep could improve subsequent alertness during a night shift. Improving the wakefulness of night-shift workers over the nighttime could result in substantial benefits for the individual workers, improve workplace productivity and safety, and improve public health.

Inclusion Criteria:

• Age 20-50 (men or women)
• Current shift worker (for at least 3 months, at least 5 overnights/month and 3 consecutive)
• A willingness and ability to comply with study procedures
• If of child-bearing potential, using a medically-accepted method of birth control, including abstinence, barrier method with spermicide, steroidal contraceptive (oral, transdermal, implanted, or injected) in conjunction with a barrier method, or intrauterine device [IUD]).

Exclusion Criteria:

• Current diagnosis of DSM-IV Axis I disorder (other than insomnia)
• Regular treatment (>1time/wk) with CNS-active medication within 1 month of first inpatient visit
• Uncontrolled medical illness that would interfere with participation in the study
• BMI>32 or < 19.8 kg/m2
• Current symptoms or diagnosis of any moderate to severe sleep disorder other than SWSD
• Periodic Leg Movement of Sleep Index (PLMSi)>20/hr of sleep or Respiratory Desaturation Index (RDI)>15 on polysomnography (PSG)
• Current alcohol or drug dependence/abuse
• Menopausal or peri-menopausal symptoms that disrupt sleep
• Pregnant, lactating, or planning to become pregnant
• Current smoking of more than 10 cigarettes per day
• Current use of over the counter sleep aids such as Benadryl or melatonin

After publication of initial results, would require institutional data sharing agreement with Partners Inc (Brigham and Women's Hospital), and Dr. Buxton

Adverse events characterized as per clinicaltrials.gov standards. All event were "Other (Not Including Serious) Adverse Events: Adverse events that are not Serious Adverse Events. "

Systematic methods included regular investigator assessment.