perhaps even more interesting would be preloading with tryptophan.

melatonin represents one possible end product of tryptophan metabolism, tryptophan obviously being the starting compound. in theory, some tryptophan metabolizes into tryptamine compounds, which actually inhibit production of serotonin (which would metabolize into n-acetyl-serotonin, then melatonin); so it would  make more sense to load up on the precursor in the whole pathway...tryptophan.