5-methoxypsoralen (5-MOP) stimulates pineal melatonin secretion, and a
decrease in dark phase melatonin levels has been described in major d
epression. As exogenous melatonin has shown synchronizer properties, a
uthors hypothesized that giving 5-MOP would have antidepressant proper
ties. Twenty-six inpatients meeting the criteria of major depressive d
isorders were enrolled in a four-week, double blind trial of 5-MOP ver
sus amitriptyline. Clinical improvement was identical in both treatmen
t groups but biological changes were different in each group: 5-MOP pa
tients showed an early nocturnal surge of melatonin levels that was ma
intained at the fourth treatment week, while melatonin levels remained
unchanged in patients treated with amitriptyline.