Melatonin Effects on Sleep:
1. Sleep-phase alteration - Melatonin is excreted during the absence of light exposure and influences the timing of the SCN. If taken late in the evening it advances the next phase of sleep. If it is taken in the morning is causes a delay in the next phase of sleep.
2. Hypnotic Effect - Melatonin is a mild hypnotic when given in the day at the time when levels are low. Causes the body temperature to decrease. Usually associated with sleep onset.
3. Other actions - Vasoconstrictor, has a slight hypotensive effect.