Background: The aim of this study was to determine whether there are differences in the 24-hour melatonin secretion profile between patients with major depression (MD) before and after clomipramine treatment, and a control group, and also whether or not there exist statistically significant differences in the melatonin levels depending on the severity of depression.
Material/Methods: 20 patients with MD and 14 healthy volunteers took part in the study. Before and after clomipramine treatment all the patients had an 8ml blood sample collected 7 times, at fixed hours, for measurement of the melatonin level. The severity of depression was assessed (HAMDS, BDI, POMS) before and after treatment.
Results: The mean melatonin concentration at each of the chosen hours was higher in persons with MD than in the control, but the differences reached statistical significance only at certain night hours. In both groups the nocturnal rise in melatonin secretion began at 12 midnight, reaching its peak at 2 am, to reach low values by 8 am, similar to the values from the previous morning. After 8 weeks of clomipramine treatment, the melatonin concentrations at 12 midnight, 2 am, and 4 am were lowered, and were elevated at 8 am, 2 pm, and 8 pm. The difference was statistically significant only at 8 pm. Melatonin secretion during both night time hours and daytime hours is higher in individuals with MD than in healthy subjects, and remains elevated after 8 weeks of effective clomipramine treatment. Those patients whose state changed the least after 8 weeks of clomipramine treatment differed in a statistically significant way in terms of melatonin secretion level at 2 pm from those patients who improved the most.
Conclusions: Some patients with MD have elevated melatonin concentration levels during daytime and nighttime hours, and this melatonin secretion pattern is independent of the severity of depression.

Keywords: major depression, melatonin concentration