Plasma melatonin levels in depressed patients before and after treatment with antidepressant medication

Daytime melatonin was measured by radioimmunoassay in 113 depressed outpatients before and after treatment with imipramine, mianserin, phenelzine, and placebo. At baseline, elevation of daytime melatonin values above expected levels suggests nonspecificity of the assay. After 6 weeks of treatment, melatonin levels were somewhat lower in patients on imipramine, mianserin, and placebo and slightly increased in patients treated with phenelzine. Changes in melatonin levels during treatment were significantly different for phenelzine compared with the other treatments. These findings are consistent with alterations in beta-adrenergic functioning or changes in serotonin levels.