Abstract
Dear Sir The results of the study of Perez and Rozen (1) suggest that melatonin can be used in the prevention of chronic cluster headache. The authors administered melatonin at 21:00 h without knowledge of the endogenous melatonin rhythm.
Melatonin is a chronobiotic drug, which advances circadian rhythms most when administered 5 h before melatonin onset (2). It delays circadian rhythms most, when administered 10 h after melatonin onset (2). So administration of melatonin, without knowledge of the individual's endogenous melatonin onset, may result in adverse effects on circadian rhythms including sleep–wake, temperature and cortisol rhythm. Endogenous melatonin onset can be measured easily in saliva (3).
Consequently we suggest prescribing melatonin merely to patients with known endogenous melatonin onset.