The effects of melatonin on circadian phase depend on the time at which it is administered, and are generally opposite those of light. Specifically, melatonin given in the evening results in an advance of the circadian system to an earlier hour ("phase advance"). While melatonin appears to be useful in the treatment of sleep disruption in the blind, the phase shifting ability of native melatonin is much less than that of light, limiting its utility in the treatment of circadian dysfunction in sighted individuals.