Endpoint

Sleep onset latency

The time it takes to reach REM sleep. It is typically measured by polysomnography or EEG as a part of various sleep pattern tests (e.g., multiple sleep latency test).

Definition from MeSH (D000074361), National Library of Medicine, read 2026-09-23. NLM revises MeSH; this copy may not reflect its current record.

CAT:outcome/sleep-onset-latencyreported in minutes12 findings from 2 compounds

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What moved it

How to read these marks

12 findings · 2 compounds · 1 null · by evidence strength

Compound	Direction	Findings	Strongest evidence
melatonin	down 9 · no effect 1	10	Evidence strength: moderate. Human evidence with one recorded weakness, or capped at moderate by its design or by unread numbers.
caffeine	up	2	Evidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.

Reported to move it

11 findings

melatonin — decreases
ModerateEvidence strength: moderate. Human evidence with one recorded weakness, or capped at moderate by its design or by unread numbers.Findingreplicated ×8
“The pooled SMD in healthy subjects showed that exogenous melatonin significantly decreased SOL compared to placebo.”
Quoted verbatim from Melatonergic agents influence the sleep-wake and circadian rhythms in healthy and psychiatric participants: a systematic review and meta-analysis of randomized controlled trials..
Study

meta-analysis
Population

Healthy adult participants; pooled RCTs of exogenous melatonin vs placebo, sleep onset latency by polysomnography or actigraphy
Melatonergic agents influence the sleep-wake and circadian rhythms in healthy and psychiatric participants: a systematic review and meta-analysis of randomized controlled trials.2022PMID:35115662Permalink
melatonin — decreases
ModerateEvidence strength: moderate. Human evidence with one recorded weakness, or capped at moderate by its design or by unread numbers.Findingreplicated ×8
“Our meta-analysis demonstrated melatonin had a significant benefit in reducing sleep latency.”
Quoted verbatim from Meta-analysis: melatonin for the treatment of primary sleep disorders..
Study

meta-analysis
Population

Adults and children with primary sleep disorders (insomnia, delayed sleep phase syndrome, REM sleep behaviour disorder) in placebo-controlled trials; primary outcome; fixed-effects pooled estimate, latency measured by polysomnography/actigraphy or by sleep diary depending on trial
Meta-analysis: melatonin for the treatment of primary sleep disorders.2013PMID:23691095Permalink
melatonin — decreases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×8
“In the 20 patients who completed the study, sleep onset latency was significantly reduced while subjects were taking melatonin as compared with both placebo and baseline.”
Quoted verbatim from A randomized, double-blind, placebo-controlled crossover study of the effect of exogenous melatonin on delayed sleep phase syndrome..
Study

crossover
Participants

20
Duration

4 weeks
Dose

melatonin 5 mg, taken 19:00-21:00
Population

22 patients (20 completed) with delayed sleep phase syndrome, nocturnal sleep restricted to 24:00-08:00, polysomnography
A randomized, double-blind, placebo-controlled crossover study of the effect of exogenous melatonin on delayed sleep phase syndrome.2001PMID:11211063Permalink
melatonin — decreases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×8
“Melatonin decreased sleep-onset latency by 23.27 minutes (95% CI: 4.83 -41.72 min).”
Quoted verbatim from The use of exogenous melatonin in delayed sleep phase disorder: a meta-analysis..
Study

meta-analysis
Population

adults and children with delayed sleep phase disorder
The use of exogenous melatonin in delayed sleep phase disorder: a meta-analysis.2010PMID:21120122Permalink
melatonin — decreases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×8
“Quantitative measures were appropriate with significant reductions in sleep onset latency (n = 6) in the melatonin condition relative to the placebo condition (p = 0.003), and bedtime resistance (n = 8) according to the CSHQ (p = 0.004).”
Quoted verbatim from A Pilot Randomised Controlled Trial of Sublingual Melatonin for Sleep Onset Insomnia in Children With Foetal Alcohol Spectrum Disorder (FASD)..
Study

crossover
Participants

6
Duration

3 weeks
Population

children with sleep onset delay, 'at risk' of or diagnosed with foetal alcohol spectrum disorder (FASD)
A Pilot Randomised Controlled Trial of Sublingual Melatonin for Sleep Onset Insomnia in Children With Foetal Alcohol Spectrum Disorder (FASD).2026PMID:41122831Permalink
melatonin — decreases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×8
“Dose-response meta-analysis showed that melatonin gradually reduces sleep onset latency and increases total sleep time, peaking at 4 mg/day.”
Quoted verbatim from Optimizing the Time and Dose of Melatonin as a Sleep-Promoting Drug: A Systematic Review of Randomized Controlled Trials and Dose-Response Meta-Analysis..
Study

meta-analysis
Population

patients with insomnia and healthy volunteers
Optimizing the Time and Dose of Melatonin as a Sleep-Promoting Drug: A Systematic Review of Randomized Controlled Trials and Dose-Response Meta-Analysis.2024PMID:38888087Permalink

Show the remaining 5

caffeine — increases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×1
“Caffeine consumption reduced total sleep time by 45 min and sleep efficiency by 7%, with an increase in sleep onset latency of 9 min and wake after sleep onset of 12 min.”
Quoted verbatim from The effect of caffeine on subsequent sleep: A systematic review and meta-analysis..
Study

meta-analysis
Population

meta-analysis of 24 studies on the effect of caffeine consumption on subsequent night-time sleep
The effect of caffeine on subsequent sleep: A systematic review and meta-analysis.2023PMID:36870101Permalink
melatonin — decreases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×8
“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.”
Quoted verbatim from The effect of prolonged-release melatonin on sleep measures and psychomotor performance in elderly patients with insomnia..
Study

RCT
Duration

3 weeks
Dose

prolonged-release melatonin 2 mg nightly
Population

Adults aged 55 years and older with primary insomnia (DSM-IV)
The effect of prolonged-release melatonin on sleep measures and psychomotor performance in elderly patients with insomnia.2009PMID:19584739Permalink
melatonin — decreases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×8
“Melatonin treatment significantly reduced sleep onset latency by 4.0 min (95% CI 2.5, 5.4); increased sleep efficiency by 2.2% (95% CI 0.2, 4.2), and increased total sleep duration by 12.8 min (95% CI 2.9, 22.8).”
Quoted verbatim from Effects of exogenous melatonin on sleep: a meta-analysis..
Study

meta-analysis
Population

adults in exogenous-melatonin sleep trials; meta-analysis of 17 studies (mixed healthy and clinical populations)
Effect 4 mean difference, 95% CI 2.5 to 5.4
Effects of exogenous melatonin on sleep: a meta-analysis.2005PMID:15649737Permalink
melatonin — decreases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×8
“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).”
Quoted verbatim from Efficacy of prolonged release melatonin in insomnia patients aged 55-80 years: quality of sleep and next-day alertness outcomes..
Study

RCT
Duration

3 weeks
Dose

prolonged-release melatonin (Circadin) 2 mg once daily, 2 h before bedtime
Population

Adults aged 55-80 years with primary insomnia
Efficacy of prolonged release melatonin in insomnia patients aged 55-80 years: quality of sleep and next-day alertness outcomes.2007PMID:17875243Permalink
caffeine — increases
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.Findingreplicated ×1
“Random-effects meta-analysis showed that caffeine significantly reduced total sleep time (mean difference [MD] = -34.67 min), sleep efficiency (MD = -4.74 %), and slow-wave sleep proportions (SWS%) (MD = -1.01 %), while prolonging sleep onset latency (MD = +8.35 min).”
Quoted verbatim from Age- and dose-specific effects of caffeine on sleep: A meta-analysis of controlled crossover trials..
Study

meta-analysis
Population

Healthy adults; acute caffeine versus placebo, nighttime polysomnography. Overall pooled estimate across 22 controlled crossover trials, not an age or dose subgroup. Instrument: polysomnography.
Age- and dose-specific effects of caffeine on sleep: A meta-analysis of controlled crossover trials.2025PMID:41124973Permalink

Measured, no effect detected

1 finding

melatonin — no detected effect on
Very limitedEvidence strength: very limited. Human evidence with major recorded weaknesses, or non-human, uncontrolled or unverified evidence.FindingNull result
“Nine randomised controlled trials with 427 participants showed no evidence that melatonin had an effect on sleep onset latency in people who had sleep disorders accompanying sleep restriction (-1.0 (-2.3 to 0.3) min).”
Quoted verbatim from Efficacy and safety of exogenous melatonin for secondary sleep disorders and sleep disorders accompanying sleep restriction: meta-analysis..
Study

meta-analysis
Participants

427
Population

people with sleep disorders accompanying sleep restriction
Efficacy and safety of exogenous melatonin for secondary sleep disorders and sleep disorders accompanying sleep restriction: meta-analysis.2006PMID:16473858Permalink

How it is measured

Interval from lights-out to the first epoch of persistent sleep, by polysomnography, actigraphy or sleep diary, with the instrument recorded with each finding.

Measured, not recorded

Subject: sleep onset latency
Measurements: 5 measurements
Recorded as a finding: No

Show what was measured

Sleep onset latency
increases
Caffeine typically prolonged sleep latency, reduced total sleep time and sleep efficiency, and worsened perceived sleep quality.
PMID:26899133 · one of two readings recorded this
sleep onset latency
decreases, p = 0.037, n = 64
Sleep onset latency (min) | 28.06 ± 27.46 | 21.02 ± 17.45 |.037
PMID:38764237 · one of two readings recorded this
Sleep onset latency
decreases
The dose–response model proposed by Cruz-Sanabria et al. (2024) showed that taking 4 mg/day of exogenous melatonin is most effective in reducing sleep onset latency (SOL)
PMID:40507048 · one of two readings recorded this
sleep onset latency
increases
Random-effects meta-analysis showed that caffeine significantly reduced total sleep time (mean difference [MD] = -34.67 min), sleep efficiency (MD = -4.74 %), and slow-wave sleep proportions (SWS%) (MD = -1.01 %), while prolonging sleep onset latency (MD = +8.35 min)
PMID:41124973 · one of two readings recorded this
sleep onset latency
no effect, p = 0.11
sleep onset latency (MD: −1.07, 95% CI: −2.37 to 0.24, P =.11, I2 = 86%; Fig. 4)
PMID:42410839 · one of two readings recorded this

Sources cited

12 papers

Subject: sleep onset latency
Findings: 12
Papers: 12

Compound

Direction

Findings

Strongest evidence

melatonin

down 9 · no effect 1

caffeine

Measured, not recorded

Subject

sleep onset latency

Measurements

5 measurements

Recorded as a finding

Show what was measured

Sleep onset latency
increases
Caffeine typically prolonged sleep latency, reduced total sleep time and sleep efficiency, and worsened perceived sleep quality.
PMID:26899133 · one of two readings recorded this
sleep onset latency
decreases, p = 0.037, n = 64
Sleep onset latency (min) | 28.06 ± 27.46 | 21.02 ± 17.45 |.037
PMID:38764237 · one of two readings recorded this
Sleep onset latency
decreases
The dose–response model proposed by Cruz-Sanabria et al. (2024) showed that taking 4 mg/day of exogenous melatonin is most effective in reducing sleep onset latency (SOL)
PMID:40507048 · one of two readings recorded this
sleep onset latency
increases
Random-effects meta-analysis showed that caffeine significantly reduced total sleep time (mean difference [MD] = -34.67 min), sleep efficiency (MD = -4.74 %), and slow-wave sleep proportions (SWS%) (MD = -1.01 %), while prolonging sleep onset latency (MD = +8.35 min)
PMID:41124973 · one of two readings recorded this
sleep onset latency
no effect, p = 0.11
sleep onset latency (MD: −1.07, 95% CI: −2.37 to 0.24, P =.11, I2 = 86%; Fig. 4)
PMID:42410839 · one of two readings recorded this