| dc.description.abstract | Cluster headache (CH) has been associated with circadian disturbances. The present systematic review examined available evidence for the utilization of melatonin (MT) in CH prophylaxis. First, case-control studies assessing nocturnal MT or its urine-expelled metabolite 6-sulfatoxymelatonin (aMT6s) in CH individuals and healthy controls (HC) were reviewed and meta-analyzed. Secondly, the results from randomized controlled trials (RCTs) and non-randomized studies evaluating MT’s use in the prevention of CH were discussed. Literature search included MEDLINE, EMBASE, CENTRAL, PsycINFO, trial registries, Google Scholar, and OpenGrey. Bouts and remissions were assessed separately. Ten case-control studies (adult participants) were retrieved. Seven evaluated serum MT; meta-analysis involved only three of them (due to deficient reporting, n: bout = 31, remission = 38, HC = 31). Results were compatible with lower nocturnal serum MT levels during bouts [bout-HC; FE-MD = −29.89 pg/mL, 95% CI = (−46.00, −13.78), remission-HC; FE-MD = −2.40 pg/mL, 95% CI = (−16.57, 21.38), bout-remission; RE-MD = −32.10 pg/mL, 95% CI = (−56.78, −7.42)]. Nocturnal urinary melatonin was appraised in two studies, but reporting issues impeded the capitalization of the results. Nocturnal urine aMT6s was evaluated by two studies (n: bout = 29, remission = 22, HC = 20), and pooled results were indicative of lower aMT6s concentration in CH individuals during both active and inactive periods [bout-HC; FE-MD = −9.63 μg/nocturnal urine collection, 95% CI = (−14.40, −4.85), remission-HC; FE-MD = −9.12 μg/nocturnal urine collection, 95% CI = (−14.63,-3.62), bout-remission; FE-MD = −0.58 μg/nocturnal urine collection, 95% CI = (−4.58, 3.42)]. Regarding CH prophylaxis, one RCT and two non-randomized trials were retrieved, involving a total of 41 adult CH individuals (11—episodic, 31—chronic) and rendering the deduction of any conclusions precarious. Overall, available data for the role use of MT in CH are insufficient and inconclusive. Complementary studies evaluating endogenous MT concentrations and MT administration to patients with CH are warranted. © 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd | en |