Plasma concentrations of melatonin in man following oral absorption of different preparations.

The plasma concentrations of melatonin in man, fasting and fed, were determined after ingestion of three different oral preparations. A dose of 2 mg was given as either a gelatine capsule, a solution in corn oil or as a slow-release pill. Gelatine capsules and the corn oil preparation gave reproducibly timed peak plasma concentrations, 30 to 60 min after ingestion regardless of nutritional status, and plasma melatonin remained at or above endogenous night-time levels for 3-4 h with mean elimination half-lives of 0.54 to 0.67 h. The slow-release preparation usefully extended high plasma melatonin concentrations for 5-7 h after ingestion but the timing of peak concentrations was very dependent on nutritional status. These preparations should be of use in the study of timed melatonin administration in man.