Influence of melatonin on fatigue severity in patients with chronic fatigue syndrome and late melatonin secretion

The effect of melatonin, a chronobiotic drug, was explored in 29 patients with chronic fatigue syndrome (CFS) and Dim Light Melatonin onset (DLMO) later than 21.30 hours, reflective of delayed circadian rhythmicity. The patients took 5 mg of melatonin orally, 5 h before DLMO during 3 months. Their responses to the checklist individual strength (CIS), a reliable questionnaire measuring the severity of personally experienced fatigue, were assessed twice with a 6‐week interval immediately before the treatment and once after 3 months treatment. In the pre‐treatment period the fatigue sub‐score improved significantly. After treatment, the total CIS score and the sub‐scores for fatigue, concentration, motivation and activity improved significantly. The sub‐score fatigue normalized in two of the 29 patients in the pre‐treatment period and in eight of 27 patients during treatment. This change was significant. In the patients with DLMO later than 22.00 hours ( n = 21) the total CIS score and the sub‐scores for fatigue, concentration and activity improved significantly more than in the patients ( n = 8) with DLMO earlier than 22.00 hours. Melatonin may be an effective treatment for patients with CFS and late DLMO, especially in those with DLMO later than 22.00 hours.