From "Alcohol's Effects on Sleep in Alcoholics" by Kirk J. Brower, M.D.
"A brain chemical implicated in sleep regulation is melatonin. Supplemental melatonin has been used with mixed results to treat insomnia but appears most effective in people whose internal (i.e., endogenous) melatonin levels are low (Stone et al. 2000). Some studies suggest that melatonin levels are decreased in alcoholics (Schmitz et al. 1996; Wetterberg et al. 1992); accordingly, supplemental melatonin could be investigated for the treatment of alcoholic patients with both insomnia and low levels of endogenous melatonin."