Melatonin SR (Sustained Release) Clinical Evidence

Prolonged-release melatonin for children with neurodevelopmental disorders.
De Leersnyder H1, Zisapel N, Laudon M.

2011 Jul;45(1):23-6. doi: 10.1016/j.pediatrneurol.2011.02.001.

Abstract:

Previous studies demonstrated the efficacy and safety of prolonged-release melatonin in children and adolescents with neurodevelopmental and behavioral disorders. The long-term effectiveness and safety of prolonged-release melatonin treatment were assessed in 88 children (42 girls and 46 boys) with neurodevelopmental disorders. These patients participated in a compassionate-use program with the drug Circadin (2 mg; Neurim Pharmaceuticals, Tel Aviv, Israel) in France, and received treatment in the context of regular care by a specialized physician. The study involved a structured questionnaire for the parents, comprising a combination of multiple-choice and numeric questions addressing sleep onset/offset, sleep quality problems, and mood. The dose of melatonin ranged from 4-6 mg, and treatment duration ranged from 6-72 months. Within 3 months, sleep latency with prolonged-release melatonin decreased by 44.0% (P < 0.001), sleep duration increased by 10.1% (P < 0.001), the number of awakenings decreased by 75% (P < 0.001), and sleep quality improved by 75%, compared with baseline (P < 0.001). No serious adverse events or treatment-related comorbidities were reported. Prolonged-release melatonin remains a safe, effective therapy for the long-term treatment of sleep disorders in children with neurodevelopmental disorders.
Copyright © 2011 Elsevier Inc. All rights reserved.

Commented In: 

Effects of melatonin should be studied separately in each neurodevelopmental disorder and with specific sleep diagnoses. [Pediatr Neurol. 2012]
PMID: 21723455 DOI: 10.1016/j.pediatrneurol.2011.02.001
[PubMed – indexed for MEDLINE]

Phase advance with separate and combined melatonin and light treatment.
Paul MA1, Gray GW, Lieberman HR, Love RJ, Miller JC, Trouborst M, Arendt J.

2011 Mar;214(2):515-23. doi: 10.1007/s00213-010-2059-5. Epub 2010 Nov 11.

Introduction:

Melatonin and light treatment are recommended for hastening adaptation to time zone change. We evaluated an afternoon regimen of 3 mg sustained release (SR) melatonin with and without next morning green light treatment for circadian phase advance. Effects of melatonin and light were tested separately and then combined to determine if the total phase change is additive or synergistic.

Material and Methods: 

For each condition (melatonin, placebo, light, melatonin plus light), 11 subjects spent from Tuesday evening until Friday afternoon in the laboratory. For all four conditions, the following sleep schedule was maintained: night 1, 2345 to 0630 hours, night 2, 1600 to 0530 hours, and night 3, 2345 to 0700 hours. For the light-only condition, light treatment was administered between 0700 and 0800 hours on Thursday. For melatonin-only or placebo conditions, capsules were administered at 1600 hours on Wednesday. For the combined condition, melatonin was administered at 1600 hours on Wednesday with light treatment between 0600 and 0700 hours on Thursday. Circadian phase was assessed by calculating dim light melatonin onset (DLMO) from salivary melatonin, using a mean baseline +2 standard deviations (BL+2 SD) threshold. For all four conditions, pre-treatment and post-treatment DLMO assessments were on Tuesday and Thursday evenings, respectively.

Results:

Phase advances were: melatonin at 1600 hours, 0.72 h p<0.005, light treatment from 0700 to 0800 hours, 0.31 h, non-significant, and the combined treatment, 1.04 h p<0.0002.

Conclusions:

The phase advance from the combination of afternoon melatonin with next morning light is additive.

Prolonged release melatonin in the treatment of primary insomnia: evaluation of the age cut-off for short- and long-term response.
Wade AG, Crawford G, Ford I, McConnachie A, Nir T, Laudon M, Zisapel N.

2011 Jan;27(1):87-98. doi: 10.1185/03007995.2010.537317. Epub 2010 Nov 24.

Source:

CPS Research, Glasgow, UK. [email protected]

Objectives: 

The authors recently reported on efficacy and safety of prolonged-release melatonin formulation (PRM; Circadin 2  mg) in elderly insomnia patients. The age cut-off for response to PRM and the long-term maintenance of efficacy and safety were further evaluated by looking at the total cohort (age 18-80 years) from that study and subsets of patients aged 18-54 and 55-80 years (for whom the drug is currently indicated).

Design: 

Randomised, double-blind, placebo controlled trial. Setting: Multicentre, outpatients, primary care setting.

Methods: 

A total of 930 males and females aged 18-80 years with primary insomnia who reported mean nightly sleep latency (SL) >20  min were enrolled and 791 entered the active phase of the study. The study comprised a 2-week, single-blind placebo run-in period followed by 3 week’s double-blind treatment with PRM or placebo, one tablet per day at 2 hours before bedtime. PRM patients continued whereas placebo completers were re-randomised 1:1 to PRM or placebo for 26 weeks followed by 2-weeks run-out on placebo. Main outcome measures: SL and other sleep variables derived from sleep diary, Pittsburgh Sleep Quality Index (PSQI), Quality of life (WHO-5), Clinical Global Impression of Improvement (CGI-I) and adverse effects, recorded each visit, withdrawal and rebound effects during run-out.

Results: 

In all, 746 patients completed the 3-week and 555 (421 PRM, 134 placebo) completed the 6-month period. The principal reason for drop-out was patient decision. At 3 weeks, significant differences in SL (diary, primary variable) in favour of PRM vs. placebo treatment were found for the 55-80-year group (-15.4 vs. -5.5  min, p = 0.014) but not the 18-80-year cut-off which included younger patients. Other variables (SL-PSQI, PSQI, WHO-5, CGI-I scores) improved significantly with PRM in the 18-80-year population, more so than in the 55-80-year age group. Improvements were maintained or enhanced over the 6-month period with no signs of tolerance. No withdrawal symptoms or rebound insomnia were detected. Most adverse events were mild with no significant differences between PRM and placebo groups in any safety outcome.

Conclusions: 

The results demonstrate short- and long-term efficacy of PRM in insomnia patients aged 18-80 years, particularly those aged 55 and over. PRM was well-tolerated over the entire 6-month period with no rebound or withdrawal symptoms following discontinuation. Study Registry No: ClinicalTrials.gov ID: NCT00397189.
PMID:
21091391

Nightly treatment of primary insomnia with prolonged release melatonin for 6 months: a randomized placebo controlled trial on age and endogenous melatonin as predictors of efficacy and safety.
Wade AG, Ford I, Crawford G, McConnachie A, Nir T, Laudon M, Zisapel N.

2010 Aug 16;8:51. doi: 10.1186/1741-7015-8-51.

Source:

CPS Research, Glasgow, UK. [email protected]

Background: 

Melatonin is extensively used in the USA in a non-regulated manner for sleep disorders. Prolonged release melatonin (PRM) is licensed in Europe and other countries for the short term treatment of primary insomnia in patients aged 55 years and over. However, a clear definition of the target patient population and well-controlled studies of long-term efficacy and safety are lacking. It is known that melatonin production declines with age. Some young insomnia patients also may have low melatonin levels. The study investigated whether older age or low melatonin excretion is a better predictor of response to PRM, whether the efficacy observed in short-term studies is sustained during continued treatment and the long term safety of such treatment.

Methods: 

Adult outpatients (791, aged 18-80 years) with primary insomnia, were treated with placebo (2 weeks) and then randomized, double-blind to 3 weeks with PRM or placebo nightly. PRM patients continued whereas placebo completers were re-randomized 1:1 to PRM or placebo for 26 weeks with 2 weeks of single-blind placebo run-out. Main outcome measures were sleep latency derived from a sleep diary, Pittsburgh Sleep Quality Index (PSQI), Quality of Life (World Health Organzaton-5) Clinical Global Impression of Improvement (CGI-I) and adverse effects and vital signs recorded at each visit.

Results: 

On the primary efficacy variable, sleep latency, the effects of PRM (3 weeks) in patients with low endogenous melatonin (6-sulphatoxymelatonin [6-SMT] <or=8 microg/night) regardless of age did not differ from the placebo, whereas PRM significantly reduced sleep latency compared to the placebo in elderly patients regardless of melatonin levels (-19.1 versus -1.7 min; P = 0.002). The effects on sleep latency and additional sleep and daytime parameters that improved with PRM were maintained or enhanced over the 6-month period with no signs of tolerance. Most adverse events were mild in severity with no clinically relevant differences between PRM and placebo for any safety outcome.

Conclusions: 

The results demonstrate short- and long-term efficacy and safety of PRM in elderly insomnia patients. Low melatonin production regardless of age is not useful in predicting responses to melatonin therapy in insomnia. The age cut-off for response warrants further investigation.
Comment in
• [Melatonin: effective in the elderly for treatment of primary insomnia]. [Praxis (Bern 1994). 2010]
PMID:
20712869
[PubMed – indexed for MEDLINE]

The effect of prolonged-release melatonin on sleep measures and psychomotor performance in elderly patients with insomnia.
Luthringer R, Muzet M, Zisapel N, Staner L.

2009 Sep;24(5):239-49. doi: 10.1097/YIC.0b013e32832e9b08.

Source: 

FORENAP Pharma, Rouffach, France.

Abstract: 

Objectives of this study were to investigate the effects of prolonged-release melatonin 2 mg (PRM) on sleep and subsequent daytime psychomotor performance in patients aged > or =55 years with primary insomnia, as defined by fourth revision of the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association. Patients (N = 40) were treated nightly single-blind with placebo (2 weeks), randomized double-blind to PRM or placebo (3 weeks) followed by withdrawal period (3 weeks). Sleep was assessed by polysomnography, all-night sleep electroencephalography spectral analysis and questionnaires. Psychomotor performance was assessed by the Leeds Psychomotor Test battery. By the end of the double-blind treatment, the PRM group had significantly shorter sleep onset latency (9 min; P = 0.02) compared with the placebo group and scored significantly better in the Critical Flicker Fusion Test (P = 0.008) without negatively affecting sleep structure and architecture. Half of the patients reported substantial improvement in sleep quality at home with PRM compared with 15% with placebo (P = 0.018). No rebound effects were observed during withdrawal. In conclusion, nightly treatment with PRM effectively induced sleep and improved perceived quality of sleep in patients with primary insomnia aged > or =55 years. Daytime psychomotor performance was not impaired and was consistently better with PRM compared with placebo. PRM was well tolerated with no evidence of rebound effects.
PMID:
19584739

Effects of prolonged-release melatonin, zolpidem, and their combination on psychomotor functions, memory recall, and driving skills in healthy middle aged and elderly volunteers.
Otmani S, Demazières A, Staner C, Jacob N, Nir T, Zisapel N, Staner L.

2008 Dec;23(8):693-705. doi: 10.1002/hup.980.

Source: 

FORENAP-Institute for Research in Neurosciences, Rouffach, France. [email protected]

Background:

Melatonin is an important regulator of the sleep-wake cycle. A prolonged-release formulation of melatonin (PR-M) that essentially mimics the profile of the endogenous production of the hormone is effective in the treatment of insomnia in patients aged 55 years and older. Because hypnotics result in impairments of various cognitive skills, it is important to examine the cognitive effects associated with the use of PR-M.

Objectives and Methods: 

The effects of therapeutic oral doses of PR-M (2 mg), zolpidem (10 mg) and their combination administered at bedtime on cognitive functions in healthy subjects aged 55 years and older (12 males + 4 females, age 59.4 +/- 3.2 years) were assessed in a randomized, double-blind, placebo-controlled, and four-way crossover study. Psychomotor functions, memory recall, and driving skills were assessed at 1 and 4 h following administration and the next morning.

Results: 

Compared to placebo, PR-M alone did not impaired performances on any cognitive tasks. Zolpidem significantly impaired psychomotor and driving performance 1 h and 4 h post-dosing, and early memory recall; these impairment were exacerbated with PR-M co-administration. No effects on next morning psychomotor or driving performance were observed except that the decline in memory recall after zolpidem was more pronounced in the next day. No pharmacokinetic interactions were found.

Conclusions: 

This study extends previous researches showing impairment of cognitive functions by zolpidem within 5 h post-administration. Further, PR-M use was not found associated with impairment of psychomotor functions, memory recall, and driving skills, and point to a pharmacodynamic interaction between melatonin and GABA-A modulators.
PMID:
18763235
[PubMed – indexed for MEDLINE]

Prolonged-release melatonin improves sleep quality and morning alertness in insomnia patients aged 55 years and older and has no withdrawal effects.
Lemoine P, Nir T, Laudon M, Zisapel N.

2007 Dec;16(4):372-80.

Source: 

The Clinique Lyon-Lumière, Meyzieu, France.

Abstract: 

Melatonin, secreted nocturnally by the pineal gland, is an endogenous sleep regulator. Impaired melatonin production and complaints on poor quality of sleep are common among the elderly. Non-restorative sleep (perceived poor quality of sleep) and subsequently poor daytime functioning are increasingly recognized as a leading syndrome in the diagnostic and therapeutic process of insomnia complaints. The effects of 3-weeks prolonged-release melatonin 2 mg (PR-melatonin) versus placebo treatment were assessed in a multi-center randomized placebo-controlled study in 170 primary insomnia outpatients aged > or =55 years. Improvements in quality of sleep (QOS) the night before and morning alertness (BFW) were assessed using the Leeds Sleep Evaluation Questionnaire and changes in sleep quality (QON) reported on five categorical unit scales. Rebound insomnia and withdrawal effects following discontinuation were also evaluated. PR-melatonin significantly improved QOS (-22.5 versus -16.5 mm, P = 0.047), QON (0.89 versus 0.46 units; P = 0.003) and BFW (-15.7 versus -6.8 mm; P = 0.002) compared with placebo. The improvements in QOS and BFW were strongly correlated (Rval = 0.77, P < 0.001) suggesting a beneficial treatment effect on the restorative value of sleep. These results were confirmed in a subgroup of patients with a greater symptom severity. There was no evidence of rebound insomnia or withdrawal effects following treatment discontinuation. The incidence of adverse events was low and most side-effects were judged to be of minor severity. PR-melatonin is the first drug shown to significantly improve quality of sleep and morning alertness in primary insomnia patients aged 55 years and older-suggesting more restorative sleep, and without withdrawal symptoms upon discontinuation.
PMID:
18036082
[PubMed – indexed for MEDLINE]

Efficacy of prolonged release melatonin in insomnia patients aged 55-80 years: quality of sleep and next-day alertness outcomes.
Wade AG, Ford I, Crawford G, McMahon AD, Nir T, Laudon M, Zisapel N.

2007 Oct;23(10):2597-605.

Source: 

CPS Research, Glasgow, UK. [email protected]

Objective: 

Melatonin, the hormone produced nocturnally by the pineal gland, serves as a circadian time cue and sleep-anticipating signal in humans. With age, melatonin production declines and the prevalence of sleep disorders, particularly insomnia, increases. The efficacy and safety of a prolonged release melatonin formulation (PR-melatonin; Circadin* 2 mg) were examined in insomnia patients aged 55 years and older.

Design: 

Randomised, double blind, placebo-controlled.

Setting: 

Primary care.

Methodology: 

From 1248 patients pre-screened and 523 attending visit 1, 354 males and females aged 55-80 years were admitted to the study, 177 to active medication and 177 to placebo. The study was conducted by primary care physicians in the West of Scotland and consisted of a 2-week, single blind, placebo run-in period followed by a 3-week double blind treatment period with PR-melatonin or placebo, one tablet per day at 2 hours before bedtime.

Main Outcome Measures: 

Responder rate (concomitant improvement in sleep quality and morning alertness on Leeds Sleep Evaluation Questionnaire [LSEQ]), other LSEQ assessments, Pittsburgh Sleep Quality Index (PSQI) global score, other PSQI assessments, Quality of Night and Quality of Day derived from a diary, Clinical Global Improvement scale (CGI) score and quality of life (WHO-5 well being index).

Results: 

Of the 354 patients entering the active phase of the study, 20 failed to complete visit 3 (eight PR-melatonin; 12 Placebo). The principal reasons for drop-out were patient decision and lost to follow-up. Significant differences in favour of PR-melatonin vs. placebo treatment were found in concomitant and clinically relevant improvements in quality of sleep and morning alertness, demonstrated by responder analysis (26% vs. 15%; p = 0.014) as well as on each of these parameters separately. A significant and clinically relevant shortening of sleep latency to the same extent as most frequently used sleep medications was also found (-24.3 vs.-12.9 minutes; p = 0.028). Quality of life also improved significantly (p = 0.034).

Conclusions:

PR-melatonin results in significant and clinically meaningful improvements in sleep quality, morning alertness, sleep onset latency and quality of life in primary insomnia patients aged 55 years and over.

Trial Registration:

The trial was conducted prior to registration being introduced.
PMID:
17875243
[PubMed – indexed for MEDLINE]

Cognitive effects of exogenous melatonin administration in elderly persons: a pilot study.
Peck JS, LeGoff DB, Ahmed I, Goebert D.

2004 Jul-Aug;12(4):432-6.

Source: 

University of Hawaii, John A. Burns School of Medicine, Department of Psychiatry, 1356 Lusitania Street, 4th Floor, Honolulu, HI 96813, USA.

Objective: 

Given that circadian rhythm disruption is associated with impairments in cognitive performance similar to those found in age-related cognitive decline, the authors investigated whether exogenous melatonin administration would improve cognitive functioning in healthy elderly subjects.

Methods:

This double-blind, placebo-controlled pilot study assigned 26 healthy elderly subjects to receive either melatonin 1 mg or placebo nightly for 4 weeks. Participants completed a sleep questionnaire and a battery of cognitive tests at baseline and at 4 weeks.

Results:

Melatonin administration improved reported morning “restedness” and sleep latency after nocturnal awakening, and also improved scores on the California Verbal Learning Test-interference subtest.

Conclusions: 

Melatonin administration at a dose of 1 mg nightly may be effective in improving certain aspects of cognitive functioning and subjective reports of sleep quality in elderly subjects. It may prove to be a useful therapeutic agent in the treatment of age-related cognitive decline.
PMID:
15249281

Facilitation of benzodiazepine discontinuation by melatonin: a new clinical approach.
Garfinkel D, Zisapel N, Wainstein J, Laudon M.

1999 Nov 8;159(20):2456-60.

Source: 

Aging Research and the Department of Internal Medicine, The E. Wolfson Medical Center, Holon, Israel.

Background:

Benzodiazepines are the most frequently used drug for the treatment of insomnia. Prolonged use of benzodiazepine therapy is not recommended. However, many patients, particularly older patients, have difficulties discontinuing therapy. Melatonin, a hormone that is produced at night by the pineal gland, promotes normal sleep in humans and augments sleep induction by benzodiazepine therapy.

Objective: 

To assess whether the administration of melatonin could facilitate the discontinuation of benzodiazepine therapy in patients with insomnia.

Methods:

Thirty-four subjects receiving benzodiazepine therapy were enrolled in the 2-period study. In period 1, patients received (double-blinded) melatonin (2 mg in a controlled-release formulation) or a placebo nightly for 6 weeks. They were encouraged to reduce their benzodiazepine dosage 50% during week 2, 75% during weeks 3 and 4, and to discontinue benzodiazepine therapy completely during weeks 5 and 6. In period 2, melatonin was administered (single-blinded) for 6 weeks to all subjects and attempts to discontinue benzodiazepine therapy were resumed. Benzodiazepine consumption and subjective sleep-quality scores were reported daily by all patients. All subjects were then allowed to continue melatonin therapy and follow-up reassessments were performed 6 months later.

Results:

By the end of period 1, 14 of 18 subjects who had received melatonin therapy, but only 4 of 16 in the placebo group, discontinued benzodiazepine therapy (P = .006). Sleep-quality scores were significantly higher in the melatonin therapy group (P = .04). Six additional subjects in the placebo group discontinued benzodiazepine therapy when given melatonin in period 2. The 6-month follow-up assessments revealed that of the 24 patients who discontinued benzodiazepine and received melatonin therapy, 19 maintained good sleep quality.

Conclusions: 

Controlled-release melatonin may effectively facilitate discontinuation of benzodiazepine therapy while maintaining good sleep quality.
Comment in
• Melatonin therapy: from benzodiazepine-dependent insomnia to authenticity and autonomy. [Arch Intern Med. 1999]
PMID:
10665894

Melatonin replacement therapy of elderly insomniacs.
Haimov I, Lavie P, Laudon M, Herer P, Vigder C, Zisapel N.

1995 Sep;18(7):598-603.

Source: 

Sleep Laboratory, Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.

Abstract:

Changes in sleep-wake patterns are among the hallmarks of biological aging. Previously, we reported that impaired melatonin secretion is associated with sleep disorders in old age. In this study we investigated the effects of melatonin replacement therapy on melatonin-deficient elderly insomniacs. The study comprised a running-in, no-treatment period and four experimental periods. During the second, third and fourth periods, subjects were administered tablets for 7 consecutive days, 2 hours before desired bedtime. The tablets were either 2 mg melatonin administered as sustained-release or fast-release formulations, or an identical-looking placebo. The fifth period, which concluded the study, was a 2-month period of daily administration of 1 mg sustained-release melatonin 2 hours before desired bedtime. During each of these five experimental periods, sleep-wake patterns were monitored by wrist-worn actigraphs. Analysis of the first three 1-week periods revealed that a 1-week treatment with 2 mg sustained-release melatonin was effective for sleep maintenance (i.e. sleep efficiency and activity level) of elderly insomniacs, while sleep initiation was improved by the fast-release melatonin treatment. Sleep maintenance and initiation were further improved following the 2-month 1-mg sustained-release melatonin treatment, indicating that tolerance had not developed. After cessation of treatment, sleep quality deteriorated. Our findings suggest that for melatonin-deficient elderly insomniacs, melatonin replacement therapy may be beneficial in the initiation and maintenance of sleep.
PMID:
8552931
[PubMed – indexed for MEDLINE]

Improvement of sleep quality in elderly people by controlled-release melatonin.
Garfinkel D, Laudon M, Nof D, Zisapel N.

1995 Aug 26;346(8974):541-4.

Source: 

Day Care Unit, E Wolfson Medical Center, Holon, Israel.

Abstract:

Melatonin, produced by the pineal gland at night, has a role in regulation of the sleep-wake cycle. Among elderly people, even those who are healthy, the frequency of sleep disorders is high and there is an association with impairment of melatonin production. We investigated the effect of a controlled-release formulation of melatonin on sleep quality in 12 elderly subjects (aged 76 [SD 8] years) who were receiving various medications for chronic illnesses and who complained of insomnia. In all 12 subjects the peak excretion of the main melatonin metabolite 6-sulphatoxymelatonin during the night was lower than normal and/or delayed in comparison with non-insomniac elderly people. In a randomised, double-blind, crossover study the subjects were treated for 3 weeks with 2 mg per night of controlled-release melatonin and for 3 weeks with placebo, with a week’s washout period. Sleep quality was objectively monitored by wrist actigraphy. Sleep efficiency was significantly greater after melatonin than after placebo (83 [SE 4] vs 75 [3]%, p < 0.001) and wake time after sleep onset was significantly shorter (49 [14] vs 73 [13] min, p < 0.001). Sleep latency decreased, but not significantly (19 [5] vs 33 [7] min, p = 0.088). Total sleep time was not affected. The only adverse effects reported were two cases of pruritus, one during melatonin and one during placebo treatment; both resolved spontaneously. Melatonin deficiency may have an important role in the high frequency of insomnia among elderly people. Controlled-release melatonin replacement therapy effectively improves sleep quality in this population.
Comment in
• Improvement of sleep quality by melatonin. [Lancet. 1995]
PMID:
7658780

Sleep-inducing effects of low doses of melatonin ingested in the evening.
Zhdanova IV, Wurtman RJ, Lynch HJ, Ives JR, Dollins AB, Morabito C, Matheson JK, Schomer DL.

1995 May;57(5):552-8.

Source: 

Clinical Research Center, Massachusetts Institute of Technology, Cambridge 02142, USA.

Abstract:

We previously observed tht low oral doses of melatonin given at noon increase blood melatonin concentrations to those normally occurring nocturnally and facilitate sleep onset, as assessed using and involuntary muscle relaxation test. In this study we examined the induction of polysomnographically recorded sleep by similar doses given later in the evening, close to the times of endogenous melatonin release and habitual sleep onset. Volunteers received the hormone (oral doses of 0.3 or 1.0 mg) or placebo at 6, 8, or 9 PM. Latencies to sleep onset, to stage 2 sleep, and to rapid eye movement (REM) sleep were measured polysomnographically. Either dose given at any of the three time points decreased sleep onset latency and latency to stage 2 sleep. Melatonin did not suppress REM sleep or delay its onset. Most volunteers could clearly distinguish between the effects of melatonin and those of placebo when the hormone was tested at 6 or 8 PM. Neither melatonin dose induced “hangover” effects, as assessed with mood and performance tests administered on the morning after treatment. These data provide new evidence that nocturnal melatonin secretion may be involved in physiologic sleep onset and that exogenous melatonin may be useful in treating insomnia.
PMID:
7768078
[PubMed – indexed for MEDLINE]

The sleep-promoting and sleep/wake rhythm regulating effects of melatonin are attributed to its action on two high-affinity G-protein-coupled receptors MT(1) and MT(2), melatonin receptors present in the suprachiasmatic nucleus (SCN) of the hypothalamus. Activation of these receptors promotes dissociation of G proteins into α and β,γ dimers, which interact with various effector molecules involved in the transmission of cell signaling. In the suprachiasmatic nucleus melatonin inhibits neuronal firing via MT₁, but it phase shifts neuronal firing rhythms through activation of MT₂ melatonin receptors [Dubocovich et al. 2005]. Animal experiments carried out in rats, cats, and monkeys have revealed that melatonin has the ability to reduce sleep onset time and increase sleep duration.

http://www.ncbi.nlm.nih.gov/pubmed/19326288
http://www.medscape.com/viewarticle/780687_11