Abstract: Compositions and methods for the regulation of sleep and circadian rhythms are provided. The compositions are nutritional supplements containing melatonin and one or more vitamins that enhance the effectiveness of melatonin. Preferred vitamins include folic acid, riboflavin (vitamin B2), cobalamin (vitamin B12) or pyridoxine (vitamin B6). The compositions beneficially and advantageously regulate sleep when administered to an individual and are administered to a human or animal suffering from an irregular sleep or circadian rhythm or are administered in anticipation of the development of such an irregularity.