Fig. 2.
Normal profile of endogenous melatonin (red line) and schematic human phase response curves to light (dark blue line) and exogenous melatonin (light blue line). The y-axis on the right shows the endogenous melatonin concentration. The y-axis on the left shows the direction and relative magnitude of the phase shift following light exposure or exogenous melatonin administration at various times as presented on the x-axis. The magnitude of phase shifts will depend on the dosage used and should not be directly compared—adapted with permission from Eastman and Burgess [5] and Burgess et al. [57]