Human Phase Response Curves to Three Days of Daily Melatonin: 0.5 mg Versus 3.0 mg

Context: Phase response curves (PRCs) to melatonin exist, but none compare different doses of melatonin using the same protocol. Objective: The aim was to generate a PRC to 0.5 mg of oral melatonin and compare it to our previously published 3.0 mg PRC generated using the same protocol. Design and Setting: The study included two 5-d sessions in the laboratory, each preceded by 7–9 d of fixed sleep times. Each session started and ended with a phase assessment to measure the dim light melatonin onset (DLMO). In between were 3 d in an ultradian dim light (