How long does Melatonin 3mg
stay in your system?

A 3 mg melatonin tablet is one of the most common over-the-counter strengths, though it already exceeds the dose most circadian research identifies as optimal. For many people a smaller amount taken at the right time works as well, with less risk of next-day grogginess.

Melatonin's roughly 45-minute half-life means 3 mg falls below 1% of its starting level within about four to five hours. Any morning heaviness is therefore far more likely to come from the dose size than from melatonin still circulating in your blood.