What is the oral bioavailability of melatonin in healthy adults?

Oral administration of melatonin at doses of 2 mg and 4 mg results in an absolute systemic bioavailability of approximately 15% in healthy adult populations, indicating that the majority of the ingested compound is eliminated before reaching systemic circulation. This finding highlights the substantial reduction in active drug concentration following standard oral supplementation compared to direct intravenous administration.