The “sleep hormone” melatonin is naturally produced in your body in the subjective evening and makes you tired.1 Exogenous melatonin, i.e. melatonin supplements, can not only make you tired, too, but potently shift circadian phase.2
Time of Intake: Unlike light, melatonin advances your inner clock when taken in the afternoon (mean advance of 1.5h) and delays it the most when taken soon after awakening (mean delay of 1.3h).2
Dose: 0.5mg vs. 3.0mg did not show significantly different magnitudes of phase shift. However, the higher the dose, the earlier the supplement should be taken to unfold its maximum potential (around 2h earlier for 3.0mg compared to 0.5mg)
 Walker, M. (2017). Why we sleep: Unlocking the power of sleep and dreams. Simon and Schuster.
 Burgess, H. J., Revell, V. L., Molina, T. A., & Eastman, C. I. (2010). Human Phase Response Curves to Three Days of Daily Melatonin: 0.5 mg Versus 3.0 mg. The Journal of Clinical Endocrinology & Metabolism, 95(7), 3325–3331. https://doi.org/10.1210/jc.2009-2590