Previous studies had several notable limitations, including limited information on the specific types of drugs, confounding with tranquilizers, lack of monitoring of the quantities of drugs provided to patients, and limited data on newer short-acting hypnotics, such as
zolpidem, zaleplon, and eszopiclone (Lunesta).
To address some of the limitations of previous work, Kripke and colleagues performed a matched-cohort study based on longitudinal data from a large U.S. health system.