What are the side effects of Melatonin?

Next-morning grogginess or drowsiness, especially at higher doses Headache, dizziness, or nausea in some users Vivid dreams Stop taking it for an allergic reaction, headache, confusion or nausea

Who should avoid Melatonin?

Avoid driving and machinery for five hours after taking it Do not use during pregnancy or breastfeeding Children and adolescents without clinician guidance (Health Canada has moved pediatric sleep use toward prescription oversight) Seek practitioner advice before use with cardiovascular, immune, liver or kidney disease, seizures, asthma or diabetes

Hormone

Melatonin

The body's own sleep-timing hormone, taken as a low-dose evening supplement. Its best evidence is for shortening how long it takes to fall asleep and for re-aligning a shifted body clock (jet lag, shift work, delayed sleep phase), not as a general sedative or a cure for chronic insomnia. An evening, sleep-slot ingredient, not a daytime cognitive active.

Grade BUpdated October 12, 2026Written and fact-checked in-house against The Evidence Standard. Not a clinical review.

Please note

Educational content, not medical advice. Doses below are ranges used in research, not recommendations. Talk to a qualified clinician before starting any supplement, especially if you take medication, are pregnant, or manage a health condition.

Evidence grade: Evidence: Grade B
Studied dose range: Studied sleep doses include 0.5–5 mg, taken as needed 30–60 minutes before bedtime. The Canadian adult oral monograph allows no more than 10 mg total per day; this is a ceiling, not a starting-dose recommendation.
Time to effect: Acute: the sleep-onset effect is the same night, typically within 30–60 minutes; circadian re-alignment builds over several nights.
Best form: Plain immediate-release melatonin at a stated milligram dose; avoid high-dose (10 mg) products by default. Prolonged-release forms are studied more for sleep maintenance in older adults.

The short answer

Melatonin (Hormone) is studied for falling asleep faster (reducing sleep-onset latency) and re-aligning a shifted body clock: jet lag, shift work, delayed sleep phase. In our conservative reading of the published human research, the evidence is Grade B (moderate). Studied sleep doses include 0.5–5 mg, taken as needed 30–60 minutes before bedtime. The Canadian adult oral monograph allows no more than 10 mg total per day; this is a ceiling, not a starting-dose recommendation. Acute: the sleep-onset effect is the same night, typically within 30–60 minutes; circadian re-alignment builds over several nights. A studied dose is what trials used, not a recommended dose.

Full profile

Also known as	N-acetyl-5-methoxytryptamine
Best for	Falling asleep faster (reducing sleep-onset latency) · Re-aligning a shifted body clock: jet lag, shift work, delayed sleep phase · Occasional sleep support, evening use
Evidence grade	Grade B · Moderate: several human trials, some mixed results
Studied dose range	Studied sleep doses include 0.5–5 mg, taken as needed 30–60 minutes before bedtime. The Canadian adult oral monograph allows no more than 10 mg total per day; this is a ceiling, not a starting-dose recommendation.
Time to effect	Acute: the sleep-onset effect is the same night, typically within 30–60 minutes; circadian re-alignment builds over several nights.
Best form	Plain immediate-release melatonin at a stated milligram dose; avoid high-dose (10 mg) products by default. Prolonged-release forms are studied more for sleep maintenance in older adults.
Food sources	Tart cherries, Pistachios, Eggs and fish (trace amounts, far below a supplemental dose)

Evidence, honestly graded

Claim-specific B remains published for timing. Ferracioli-Oda 2013 disclosed public/academic support and Eli Lilly-linked fellowship and award support, with no funder role; our former blanket non-sponsor description was inaccurate. A meta-analysis of 19 randomized trials in 1,683 people (Ferracioli-Oda 2013) found melatonin reduced sleep-onset latency and modestly increased total sleep time and sleep quality versus placebo. The honest caveats that keep it at B rather than higher: the effect sizes are small (sleep onset shortened by roughly 7 minutes on average), and the American Academy of Sleep Medicine's 2017 guideline (Sateia et al.) issued a weak recommendation *against* melatonin for chronic sleep-onset or sleep-maintenance insomnia, citing low-quality evidence. Read together, the fair reading is a real, well-replicated but modest effect: strongest for sleep-onset timing and circadian realignment, weakest as a treatment for chronic insomnia. Monitoring since 2026-09-14: a conference abstract presented at the American Heart Association's 2025 Scientific Sessions (TriNetX health records; 65,414 adults prescribed melatonin for at least a year, propensity-matched against 65,414 others with insomnia) reported roughly 89% higher hazard of incident heart failure and about double the all-cause mortality over five years. We treat this as information to monitor rather than a safety signal that caps the grade, and the distinction is deliberate: it is a preliminary conference abstract rather than a peer-reviewed publication; it sees only prescribed melatonin, so over-the-counter users sit in the comparison group; and confounding by insomnia severity is likely. The safety signals that do hold grades down in this library (alpha-GPC's stroke cohort, ashwagandha's LiverTox rating) are peer-reviewed or regulator-issued. A peer-reviewed publication that survives those criticisms would trigger a grade review. Re-checked 2026-09-17: the abstract still has no peer-reviewed full publication, and the peer-reviewed work that has appeared since points the other way. A survey-weighted NHANES analysis (Khan & Lima 2026) found no significant association between recent melatonin use and prevalent cardiovascular disease or heart failure once baseline differences were accounted for, and a meta-analysis of 14 randomized trials in cardiovascular patients (Ang 2026) found no harm signal. Neither settles the question; together they make the abstract weaker rather than stronger evidence. B holds, and it remains a reason to use the lowest effective dose and to raise long-term nightly use with a clinician.

See the full grading rubric (study type, replication, population match, and dose adequacy) in The Evidence Standard.

1,474 natural health products with an active licence in Health Canada's LNHPD list Melatonin as a medicinal ingredient.

That makes Melatonin a recognized, licensable medicinal ingredient in Canada, regulated by Health Canada's Natural and Non-prescription Health Products Directorate, which issues each licensed natural health product a Natural Product Number (NPN). Search the LNHPD to verify.

Source: Health Canada Licensed Natural Health Products Database, snapshot 2026-10-18. A count of products with an active licence, not an endorsement of any health claim. This describes the ingredient's regulatory standing in Canada, not Signal State Core, which is a pre-launch concept and is not a licensed natural health product.

Side effects

Next-morning grogginess or drowsiness, especially at higher doses
Headache, dizziness, or nausea in some users
Vivid dreams
Stop taking it for an allergic reaction, headache, confusion or nausea

The full side-effect breakdown: Melatonin Side Effects: What the Research Actually Shows.

Who should avoid it or check first

Avoid driving and machinery for five hours after taking it
Do not use during pregnancy or breastfeeding
Children and adolescents without clinician guidance (Health Canada has moved pediatric sleep use toward prescription oversight)
Seek practitioner advice before use with cardiovascular, immune, liver or kidney disease, seizures, asthma or diabetes

Interactions

Avoid combining with alcohol or products that cause drowsiness
Before use, seek practitioner advice about medication for seizures, blood pressure, immune suppression, mental state or sedation, steroids or blood thinners
Fluvoxamine and other CYP1A2 inhibitors can sharply raise melatonin blood levels
May interact with anticoagulants/antiplatelets, blood-pressure and diabetes medication, and some contraceptives; discuss with a clinician

Stacks well with

Glycine (evening slot)
Magnesium L-Threonate (evening slot)

Use caution stacking with

Daytime stimulant-free focus actives (this is an evening-only ingredient)
Other sedating sleep agents without clinician guidance

What to look for on a label

Health Canada has a dedicated Melatonin (Oral) monograph (adult-only, up to 10 mg total per day), permitting sleep-onset, sleep-quality, and jet-lag / sleep-wake-cycle claims. Keep claims inside it and confirm the current monograph before filing.
Keep the evening/sleep role distinct from a daytime focus product, which is why it is not in Core.
Seek practitioner advice if sleeplessness continues beyond four weeks. The Canadian oral monograph supports as-needed use and excludes combinations with ingredients that need daily use for benefit.

References

Khan B, Lima BB (2026). Open Heart, 13(1):e004108Analysis of NHANES 1999–2018, survey-weighted with multiple imputationRecent melatonin use was not significantly associated with prevalent composite cardiovascular disease or heart failure; melatonin users differed markedly from non-users in sleep disturbance and depression.
Ang SP, Chia JE, Thirupathy U, et al. (2026). Journal of Clinical Medicine, 15(9):3444Systematic review and meta-analysis, 14 randomized trials, 1,027 participants with cardiovascular diseaseChange in left ventricular ejection fraction favoured melatonin by 3.95 percentage points; troponin and final ejection fraction did not differ significantly, and no adverse cardiac signal was reported.
Ferracioli-Oda E, Qawasmi A, Bloch MH (2013). PLoS One, 8(5):e63773Meta-analysis, 19 RCTs, n=1,683Studied dose: 0.5–10 mg (varied by trial)Reduced sleep-onset latency (~7 min) and increased total sleep time (~8 min) versus placebo, with an overall sleep-quality improvement.
Sateia MJ, Buysse DJ, Krystal AD, Neubauer DN, Heald JL (2017). Journal of Clinical Sleep MedicineClinical practice guideline (systematic evidence review)Suggested clinicians not use melatonin for chronic insomnia (weak recommendation) due to low-quality evidence.
Health Canada NNHPD: Melatonin (Oral) monograph (2024). Dedicated adult-only monograph permitting sleep-onset, sleep-quality, and jet-lag / sleep-wake-cycle claims, up to 10 mg total per day. Basis for Canadian regulatory defensibility. webprod.hc-sc.gc.ca/nhpid-bdipsn (atid=melatonin.oral2). Confirm the current version before filing.
Nnadi et al. (2025): AHA Scientific Sessions abstract 4371606. Observational analysis of TriNetX health records: 65,414 adults with insomnia prescribed melatonin for at least a year, propensity-matched to 65,414 non-users, reported ~89% higher hazard of incident heart failure and roughly double the all-cause mortality over five years (the American Heart Association newsroom reported heart failure in 4.6% vs 2.7%). Circulation 2025;152(suppl_3); doi:10.1161/circ.152.suppl_3.4371606. A conference abstract, not peer-reviewed; only prescribed melatonin was captured. The basis for this entry's monitoring status, not a grade change.
Health Canada: Melatonin–Oral, 19 December 2025. Adult oral monograph gives a total-daily ceiling, as-needed directions and risk statements.

Entries above without a linked identifier are either editorial summaries of a wider body of literature or references to a named authority (a regulator or government monograph) cited by name rather than by a single paper.

Grades and studied doses are our conservative reading of the human research, shown for education. They are not product claims, and a studied dose is not a recommended dose.

Revision history

Every change to this ingredient's evidence status, dated and explained. The full cross-library log lives at Evidence Updates.

2026-10-12Safety note
Corrected the Canadian adult limit: it is 10 mg total per day, not per dose, and it is a ceiling, not a starting dose. Added the monograph's as-needed directions, no driving for five hours after a dose, and do not use in pregnancy or breastfeeding. B holds.
2026-10-12Citation review
Corrected our description of the Ferracioli-Oda meta-analysis as non-sponsor research. It disclosed academic funding and support linked to Eli Lilly, though not from a melatonin maker, and the funders had no role in the analysis. B holds.
2026-09-17Safety note
Updated the heart-failure monitoring note. The 2025 conference abstract still has no peer-reviewed publication, and the peer-reviewed work published since points the other way: an NHANES analysis found no significant association between recent melatonin use and prevalent cardiovascular disease or heart failure once baseline differences were accounted for, and a meta-analysis of 14 randomized trials in cardiovascular patients found no harm signal. Neither settles the question, but together they make the abstract weaker evidence than when we first logged it. B holds.
2026-09-14Safety note
Monitoring note added. A 2025 American Heart Association conference abstract associated a year or more of prescribed melatonin use with higher heart-failure rates in adults with insomnia. It is observational, not peer-reviewed, and captures only prescribed use, so we record it as information to monitor rather than a safety signal that caps the grade; the grade is unchanged.
2026-07-12New profile
New profile, published at Grade B on independent (non-sponsor) evidence: a meta-analysis of 19 randomized trials found melatonin reduced sleep-onset latency and modestly increased total sleep time. Graded for sleep onset specifically — not as a daytime nootropic.

See how Melatonin compares on grade, dose, and goal in the Evidence Explorer.

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