Melatonin (oral, UK regulatory context)
Oral melatonin in the UK exists in a regulatory duality that often confuses consumers. AS A MEDICINE, oral melatonin is Prescription- Only (POM) — Circadin® (prolonged-release 2 mg) is licensed for primary insomnia in adults aged 55+, and Slenyto® for paediatric autism / Smith-Magenis sleep difficulty. AS A FOOD SUPPLEMENT, oral melatonin is NOT PERMITTED for UK retail sale — the UK Food Standards Agency position prohibits melatonin in food supplements (assimilated GB rules, post-EU-exit). The widely-cited EFSA Article 13.1 health claims (jet lag, sleep onset) are EU food-supplement claims that apply where member states permit melatonin in food supplements — they do NOT override the UK MHRA POM classification. Camden does not and cannot retail oral melatonin; this entry exists as the definitive UK regulatory-truth reference and signposts UK-lawful sleep-cluster alternatives (valerian, lemon-balm, chamomile, hops, l-theanine, magnesium glycinate).
Camden Medicals editorial · Last reviewed 11 June 2026 · Next review December 2026
- Cross-checked against
- NHS
- NICE
- BNF
- EFSA
- FSA
Camden's editorial team independently graded each health claim below on the strength of the published evidence — see the grade beside every condition.
- Class
- Amino acid
- Typical daily dose
- UK MHRA-licensed Circadin® dose: 2 mg prolonged-release once daily, taken 1–2 hours before bedtime, with or after food. Slenyto® paediatric: 2 mg starting dose, titrated to 5 mg or 10 mg as needed under specialist supervision. EFSA Article 13.1 claims (where applicable in EU food-supplement context): 0.5 mg for jet lag, 1 mg for sleep onset.
- Top use evidence
- Strong
On this page
What it is
Melatonin (chemically N-acetyl-5-methoxytryptamine) is an indoleamine hormone derived from the amino acid tryptophan via the serotonin pathway: tryptophan → 5-HTP → serotonin → N-acetylserotonin → melatonin. Endogenous synthesis happens primarily in the pineal gland; smaller amounts are produced locally in the gut, retina, skin, and bone marrow. Pineal melatonin secretion is suppressed by light (particularly the blue spectrum, ~480 nm) and rises 2–4 hours before habitual bedtime, signalling biological darkness to peripheral tissues via MT1 and MT2 receptors. Plasma melatonin peaks in the middle of the biological night and falls back toward baseline by morning.
The UK regulatory duality is the central practical point of this entry. Oral melatonin AS A MEDICINE is regulated by the MHRA as a Prescription-Only Medicine (POM). Circadin® (Flynn Pharma / Neurim Pharmaceuticals) is a prolonged-release 2 mg formulation licensed under MHRA marketing authorisation for the short-term monotherapy treatment of primary insomnia in adults aged 55 years and older, characterised by poor quality of sleep. Slenyto® (Flynn Pharma) is a paediatric prolonged-release formulation (1 mg and 5 mg strengths) licensed for the treatment of insomnia in children and adolescents aged 2–18 with autism spectrum disorder and / or Smith-Magenis syndrome where sleep hygiene measures have been insufficient. Both are POM and dispensed against prescription.
Oral melatonin AS A FOOD SUPPLEMENT is NOT PERMITTED for UK retail sale. The UK Food Standards Agency position derives from the European Food Safety Authority NDA opinions and the EU food- supplement framework, assimilated into GB rules post-EU-exit. Member states retain national discretion on whether to permit melatonin in food supplements; some (Netherlands, France, Spain, Italy, Belgium) permit OTC food-supplement melatonin at low doses. The EFSA NDA panel issued two Article 13.1 health-claim opinions that were subsequently authorised at EU level — "Melatonin contributes to the alleviation of subjective feelings of jet lag" (at 0.5 mg per serving close to expected bedtime at the destination) and "Melatonin contributes to the reduction of time taken to fall asleep" (at 1 mg per serving close to bedtime). These EU-NHC claims apply where the member state permits melatonin in food supplements; they do not override the UK MHRA POM classification.
Most oral melatonin available to UK consumers via Amazon US, US travel, or some EU online retailers is sold under US Dietary Supplement Health and Education Act (DSHEA) rules, where melatonin is treated as a dietary supplement. Doses range typically 0.5 mg to 10 mg, often as gummies. These are NOT lawful UK food supplements; personal importation is a grey area in UK rules but is not a UK retail context.
Camden does not and cannot retail oral melatonin under current UK rules. This entry exists as the definitive UK regulatory-truth reference for consumers searching "melatonin UK" and signposts Camden's UK-lawful sleep-cluster alternatives.
At a glance
- UK regulatory duality: oral melatonin AS A MEDICINE is Prescription-Only (Circadin® 2 mg prolonged-release for primary insomnia in adults 55+; Slenyto® for paediatric ASD). AS A FOOD SUPPLEMENT it is NOT PERMITTED for UK retail sale.
- EFSA substantiated two Article 13.1 claims — alleviation of jet lag (0.5 mg close to bedtime at the destination) and reduction of sleep-onset latency (1 mg close to bedtime). These EU food-supplement claims apply only where a member state permits melatonin in food supplements; they do NOT override the UK Prescription-Only classification.
- Most US over-the-counter melatonin (0.5–10 mg gummies) is sold under US dietary-supplement (DSHEA) rules. It is NOT a lawful UK food supplement; personal importation is a grey area, not a UK retail context.
- UK NHS insomnia pathway: sleep hygiene, then cognitive behavioural therapy for insomnia (CBT-I), then a short-term hypnotic under prescriber oversight. Camden cannot retail oral melatonin and signposts UK-lawful sleep-cluster alternatives instead.
What people use it for
UK adults aged 55+ with diagnosed primary insomnia (poor sleep quality)
UK-licensed pathway: Circadin® 2 mg prolonged-release, prescribed by GP for short-term use (typically up to 13 weeks). Self-supplementation with imported oral melatonin is not the recognised UK pathway. [1]
Some evidenceStrongUK paediatric patients aged 2–18 with autism spectrum disorder or Smith-Magenis syndrome and persistent sleep difficulty
UK-licensed pathway: Slenyto® prolonged-release (1 mg and 5 mg strengths), prescribed by paediatrician where sleep hygiene measures have been insufficient. Self-supplementation with imported melatonin is not the recognised UK paediatric pathway. [1]
Some evidenceStrongAdults travelling across multiple time zones considering melatonin for jet lag
Where lawful in the destination jurisdiction, EFSA has authorised the Article 13.1 jet-lag claim at 0.5 mg taken close to expected bedtime at the destination. In UK retail this claim is moot because oral melatonin is not a UK-permitted food supplement. Some travellers carry OTC melatonin purchased abroad; this is personal-use grey area and not a UK retail context. Camden cannot retail or recommend specific imported products. [6]
Some evidenceModerateUK adults with general sleep difficulty (not diagnosed insomnia)
UK NHS pathway: sleep hygiene → cognitive-behavioural therapy for insomnia (CBT-I) → short-term hypnotic under prescriber oversight where indicated. Camden's UK-lawful sleep-cluster alternatives include valerian (THR herbal), lemon-balm, chamomile, hops, l-theanine, magnesium glycinate, and glycine. None has the same direct receptor mechanism as melatonin but several have authorised UK food-supplement traditional-use registrations or EFSA Article 13.1 claims for nervous-system function. [3]
Some evidenceLimitedAdults with shift-work sleep disorder
Specialist context. UK NICE CKS insomnia covers shift-work sleep difficulty under occupational-health pathways. Some shift workers in jurisdictions where OTC melatonin is permitted use low-dose pre-sleep melatonin to align sleep with the new schedule. UK retail food-supplement melatonin is not permitted. [2]
Some evidenceLimited
How it works
Melatonin acts on MT1 and MT2 G-protein-coupled receptors expressed on the suprachiasmatic nucleus (SCN, the master circadian pacemaker in the hypothalamus) and on peripheral tissues. MT1 receptor activation in the SCN promotes sleep onset; MT2 receptor activation is involved in circadian-phase shifting. Receptor binding dampens SCN-driven alerting signals, allowing endogenous sleep-promoting pathways (adenosine accumulation, GABAergic ventrolateral preoptic nucleus activity) to become dominant.
The jet-lag mechanism is phase-shifting: taking melatonin at the target destination's local bedtime helps re-anchor the SCN to the new local light-dark cycle faster than light exposure alone. The sleep-onset mechanism is the receptor-mediated SCN dampening described above. Both endpoints are time-of-day-specific — melatonin taken at the wrong circadian phase can shift the rhythm in the wrong direction.
Pharmacokinetic note: immediate-release oral melatonin has a short half-life (about 30–50 minutes), with peak plasma levels 30–60 minutes post-dose. The Circadin® prolonged-release 2 mg formulation aims to mimic the natural overnight melatonin profile; immediate- release formulations sold abroad have a faster on/off profile that may explain the early-morning awakening occasionally reported with higher US-dose melatonin gummies.
Common myths
Myth""Melatonin is a sleep medicine sold OTC in the UK""
RealityIt is not. UK MHRA classifies oral melatonin as a Prescription- Only Medicine (Circadin® for primary insomnia adults 55+; Slenyto® paediatric ASD). UK FSA does not permit oral melatonin as a food supplement. Marketing or sale of oral melatonin OTC in the UK food-supplement channel is not lawful. [1]
Myth""Higher-dose melatonin gummies (5–10 mg) work better than 0.5–1 mg""
RealityTrial evidence suggests low-dose melatonin (0.3–1 mg) is often as effective or more effective than high-dose for sleep onset and jet lag, with fewer next-day effects (drowsiness, residual sedation, vivid dreams). High-dose US OTC gummies are a marketing convention, not a clinical optimisation. UK Circadin® licensed dose is 2 mg prolonged-release.
Myth""Melatonin is non-habit-forming so dose doesn't matter""
RealityMelatonin does not produce classical dependence or withdrawal, but timing and dose still matter — taken at the wrong circadian phase, melatonin can shift the body''s rhythm in the wrong direction. UK MHRA prescribing guidance for Circadin® specifies time of administration relative to bedtime. Self-supplementing with US-OTC gummies without circadian-timing guidance is not the same as prescriber-supervised use.
Myth""Melatonin will fix my insomnia""
RealityUK NICE CKS insomnia and NHS sleep-difficulty pathway lead with sleep hygiene measures, then cognitive-behavioural therapy for insomnia (CBT-I) — recognised as the most durable evidence- based treatment for chronic insomnia. Pharmacological options (Circadin® for adults 55+, short-term hypnotics under prescriber oversight) sit downstream of CBT-I in the pathway, not upstream of it. [2,3]
Myth""US melatonin gummies are quality-checked for dose accuracy""
RealityIndependent assay studies of US OTC melatonin gummies have reported substantial dose variability — some products contain far less or far more melatonin than the label states; some contain unlabelled serotonin. This is a contributing reason UK regulators classify melatonin as a medicine: medicinal manufacture has stricter dose-accuracy and identity requirements than US dietary-supplement manufacture.
Common online questions
Synthesised from the questions UK shoppers most often ask online about Melatonin (oral, UK regulatory context). Each answer is editorial and links to its evidence in the Sources list below.
Why can't I buy melatonin over the counter in the UK?
UK regulatory position: oral melatonin AS A MEDICINE is Prescription-Only Medicine (POM) — Circadin® for primary insomnia in adults 55+, Slenyto® for paediatric ASD sleep difficulty. AS A FOOD SUPPLEMENT it is NOT PERMITTED for UK retail sale by the Food Standards Agency. Some EU member states (Netherlands, France, Spain, Italy) permit OTC food-supplement melatonin at low doses, and the US sells it freely under DSHEA rules. UK rules are stricter for both safety and regulatory- framework reasons — oral melatonin acts on receptors and produces measurable physiological effects that the FSA considers outside the food-supplement scope. [1]
Can I bring melatonin back from the US or France for personal use?
Personal importation of small quantities of melatonin for personal use sits in a grey area of UK rules. It is not a UK retail context, and it is not a Camden Medicals retail option. Anyone considering this should be aware that imported product does not have UK MHRA marketing authorisation, that quality and dose-accuracy of US OTC melatonin gummies has been variable in independent assays, and that consistency of supply is not assured. UK NHS sleep-difficulty pathway (sleep hygiene → CBT-I → short-term hypnotic under prescriber oversight) is the recognised route for diagnosed insomnia. [3]
I read that EFSA approved melatonin for jet lag — why is it not for sale in the UK?
EFSA authorised the Article 13.1 jet-lag claim ("Melatonin contributes to the alleviation of subjective feelings of jet lag") at 0.5 mg per serving close to expected bedtime at the destination — and also a sleep-onset claim ("Melatonin contributes to the reduction of time taken to fall asleep") at 1 mg per serving. These are EU food-supplement claims that apply where member states permit melatonin in food supplements. UK rules (FSA / MHRA) classify oral melatonin as a medicine, not a food supplement, and the EU NHC claim does not override the UK medicinal classification. The two regulatory frameworks operate in parallel, and the UK one is stricter. [6,7]
What UK-lawful sleep supplements does Camden offer instead?
Camden carries UK-lawful sleep-cluster alternatives. Valerian (Valeriana officinalis) has UK Traditional Herbal Registration (THR) status under the MHRA herbal scheme. Lemon-balm and chamomile have similar THR / traditional-use registrations. L-theanine and glycine are amino-acid food supplements with modest sleep-context literature. Magnesium glycinate has the EFSA Article 13.1 claim for normal nervous-system function and is well-tolerated in evening dosing. None of these have the direct MT1/MT2 receptor mechanism that melatonin has, but several have authorised UK claims or traditional-use registrations and are lawful food supplements. Talk to your GP if sleep difficulty is persistent. [4,2]
Is topical melatonin in skincare different from oral melatonin?
Yes — topical melatonin in cosmetic formulation acts at the skin surface as a lipophilic antioxidant. Topical application bypasses the systemic POM regulatory tier; the active is in a cosmetic, not a medicine or food supplement. See topical-melatonin for the cosmetic-tier discussion. The oral and topical contexts are biochemically the same molecule but regulatorily distinct.
Can children take melatonin in the UK?
Only on prescription. Slenyto® (paediatric prolonged-release formulation) is licensed for children aged 2–18 with autism spectrum disorder or Smith-Magenis syndrome where sleep hygiene measures have been insufficient. Off-label paediatric use of adult Circadin® may be considered by paediatric specialists in selected cases. Self-supplementation with imported melatonin gummies for general childhood sleep difficulty is not the recognised UK paediatric pathway and may mask sleep-disorder diagnostics that need investigation. [1]
Can I take melatonin in pregnancy?
Defer. Melatonin crosses the placenta and is present in breastmilk; supplementation in pregnancy and lactation has limited human safety data. UK MHRA Circadin® labelling recommends against use in pregnancy and breastfeeding. Suspected sleep difficulty in pregnancy: talk to your midwife or GP first. [1]
🔬 Camden’s evidence review
The research Camden reviewed, graded on its strength. This is our own appraisal — it sits beneath the official guidance above, never above it.
Primary insomnia in adults aged 55+ (Circadin® prolonged-release 2 mg)
StrongEvidencestrongUK MHRA marketing authorisation supported by registration trials (Wade et al. 2007 / 2010) showing modest improvements in sleep latency, sleep quality, and morning alertness over 3-week and 6-month follow-up versus placebo. Effect sizes are modest; UK BNF and CKS insomnia guidance recommend short-term use (typically up to 13 weeks) with periodic re-assessment. [1,2]
Paediatric autism spectrum disorder sleep difficulty (Slenyto®)
StrongEvidencestrongUK MHRA marketing authorisation supported by registration trials (Maras et al. 2018) showing clinically meaningful sleep-onset improvement in children aged 2–17 with autism. Specialist-led paediatric prescribing context. [1]
Jet lag prevention (transmeridian travel)
ModerateEvidencemoderateCochrane review (Herxheimer 2002, updated subsequently) reported that melatonin 0.5–5 mg taken close to expected bedtime at the destination is effective in reducing jet-lag symptoms after flights crossing 5 or more time zones. EFSA Article 13.1 claim is authorised at 0.5 mg per serving. UK retail food-supplement melatonin is not permitted; this evidence is descriptive only in the UK context. [8,6]
Sleep onset latency reduction (general adult population)
ModerateEvidencemoderateEFSA Article 13.1 claim authorised at 1 mg per serving close to bedtime — "Melatonin contributes to the reduction of time taken to fall asleep". Effect sizes in trials are modest (typical reduction 10–20 minutes vs placebo). UK retail food-supplement melatonin is not permitted; the EU NHC claim does not apply in UK food-supplement context. [7]
Shift-work sleep disorder
LimitedEvidencelimitedSmall trials of low-dose pre-sleep melatonin in shift workers report modest sleep-quality improvements. UK NICE CKS insomnia covers shift-work sleep difficulty under occupational-health pathways; melatonin is not on UK retail food-supplement pathways for this context. [2]
Safety
Oral melatonin is a Prescription-Only Medicine in the UK (Circadin® for adults 55+; Slenyto® for paediatric ASD). UK food-supplement retail is NOT permitted. Anyone with persistent sleep difficulty should follow the NHS pathway: sleep hygiene → CBT-I → prescriber review. Camden carries UK-lawful sleep-cluster alternatives.
Talk to your pharmacist or GP first if you:
- You take warfarin or any vitamin-K-antagonist anticoagulant — case reports of INR increase with melatonin co-administration.
- You take fluvoxamine (SSRI) — fluvoxamine inhibits CYP1A2 strongly and can raise melatonin plasma levels several-fold.
- You take any combined oral contraceptive — synthetic oestrogens slightly raise endogenous melatonin levels.
- You take benzodiazepines, z-drugs, or other sedatives — possible additive sedation.
- You take antiepileptic medication (carbamazepine, sodium valproate) — interactions with melatonin metabolism reported.
- You drive or operate machinery — Circadin® can cause residual drowsiness; do not drive within several hours of dosing.
- You are pregnant, breastfeeding, or trying to conceive — defer. Melatonin crosses the placenta and is present in breastmilk.
- Your child has persistent sleep difficulty — paediatric melatonin is Slenyto® prescriber-only; investigate underlying causes via GP or paediatrician.
Common side effects: Drowsiness (residual next-day in some), headache, vivid dreams. Less commonly: irritability, dizziness, abdominal pain, nausea.
Pregnancy and breastfeeding
Pregnancy: defer. UK MHRA Circadin® labelling recommends against use. Melatonin crosses the placenta and limited human pregnancy safety data exists.
Lactation: defer. Melatonin is present in breastmilk; UK Circadin® labelling recommends against use.
Talk to your GP, midwife, or pharmacist before starting any supplement during pregnancy or breastfeeding.
More clinical detail (for clinicians and informed readers)
Contraindications
- Pregnancy — UK Circadin® labelling recommends against use.
- Lactation — UK Circadin® labelling recommends against use.
- Hypersensitivity to melatonin or excipients.
- Active or untreated severe hepatic impairment.
- Concurrent fluvoxamine therapy (CYP1A2 inhibition raises melatonin levels several-fold).
Drug interactions
- Fluvoxamine (SSRI) — strong CYP1A2 inhibition raises melatonin plasma levels several-fold.
- Other CYP1A2 inhibitors (ciprofloxacin, oestrogen-containing combined oral contraceptives) — raise melatonin levels.
- CYP1A2 inducers (carbamazepine, rifampicin, smoking) — reduce melatonin levels.
- Warfarin and other vitamin-K-antagonist anticoagulants — case reports of INR increase.
- Benzodiazepines and z-drugs — possible additive sedation.
- Antihypertensives — possible additive blood-pressure-lowering.
- Insulin and antidiabetic agents — possible glucose-handling changes.
- Anti-epileptic medication — interactions with metabolism reported.
This is not an exhaustive list. Always tell your prescriber and pharmacist about every supplement you take.
Common side effects
- Drowsiness — particularly with higher doses or immediate-release formulations.
- Headache.
- Vivid or unusual dreams.
- Mild GI upset.
Rare side effects
- Hypersensitivity reactions — uncommon.
- Mood changes (irritability, depressive feelings) — case reports.
- Hypotension.
- Hyperglycaemia in patients with diabetes — case reports.
How to take it
- Typical supplemental range
- UK MHRA-licensed Circadin® dose: 2 mg prolonged-release once daily, taken 1–2 hours before bedtime, with or after food. Slenyto® paediatric: 2 mg starting dose, titrated to 5 mg or 10 mg as needed under specialist supervision. EFSA Article 13.1 claims (where applicable in EU food-supplement context): 0.5 mg for jet lag, 1 mg for sleep onset.
- Timing
- UK Circadin® licensed timing: 1–2 hours before habitual bedtime. EU food-supplement context (where applicable): close to bedtime for sleep onset; close to expected destination bedtime for jet lag.
How to spot quality
Look for
- For UK customers: this is a prescriber-only context. Talk to your GP about Circadin® if you have primary insomnia and are 55+.
- For consumers travelling abroad and considering imported product: low-dose immediate-release (0.3–1 mg) generally outperforms high-dose for sleep onset, with fewer next-day effects.
- Independent third-party assay verification (e.g. NSF, USP) for any imported product — US OTC dose variability is documented.
- Product manufactured under cGMP / EU GMP certification.
- Dose declared per serving; clear timing instructions.
- Pregnancy + paediatric contraindications printed on the label.
- Drug-interaction warnings printed on the label (warfarin, fluvoxamine, contraceptives, anti-epileptics).
Red flags
- OTC sale in the UK food-supplement channel — not a lawful UK retail context.
- High-dose gummies (5–10 mg) marketed for general sleep difficulty (low-dose is generally more effective).
- Marketing as a paediatric sleep supplement (UK paediatric melatonin is Slenyto® prescriber-only).
- Unbranded / generic Chinese-source supply with no third-party assay.
- No drug-interaction warning.
- No pregnancy contraindication.
- "Natural sleep medicine" or "non-habit-forming sleep aid" framing without the regulatory caveats.
- Combination products that conceal the melatonin dose in a "proprietary blend".
Where Camden lands · gap declared
Camden does NOT and CANNOT retail oral melatonin under current UK rules. Camden cannot stock, sell, or recommend specific oral melatonin products; this entry exists as the definitive UK regulatory-truth reference. Camden carries UK-lawful sleep-cluster alternatives (valerian, lemon-balm, chamomile, hops, l-theanine, magnesium glycinate, glycine) and signposts NHS pathways for diagnosed insomnia. The SEO authority value of this entry is on the "melatonin UK" search cluster — capturing consumers searching for OTC melatonin and providing the regulatory truth + lawful alternative pointers.
Commonly combined with
Other ingredients that share a biological pathway, cofactor relationship, or evidence-backed protocol with this one. Mechanisms below cite primary physiology — not folk pairing. Doses are literature ranges, not recommendations. Talk to your pharmacist or GP before changing your stack, especially if you take prescription medication.
L-Theanine
Limited evidenceIn jurisdictions where oral melatonin is permitted as a food supplement, low-dose melatonin + l-theanine is a common evening-stack combination. In the UK food-supplement context this combination is moot because oral melatonin is not permitted; l-theanine alone is a UK-lawful alternative.
Melatonin acts on MT1/MT2 receptors to dampen SCN-driven alerting and promote circadian-darkness signalling. L-theanine is an amino acid that modestly raises GABA, dopamine, and serotonin and reduces alpha-wave EEG arousal. The mechanisms are non-overlapping and the combination has narrative additive logic. Pivotal-trial evidence for the combination outperforming either alone is limited.
Evidence: Both ingredients individually have small sleep-context trial bodies of evidence. Combination has not been the subject of pivotal UK trials. UK retail combination is not lawful (oral melatonin is POM).
Doses studied: Where lawful in the destination jurisdiction: melatonin 0.5–1 mg + l-theanine 100–200 mg evening dose. Not a UK retail context.
Magnesium
Limited evidenceMagnesium glycinate is a frequent UK-lawful evening sleep-cluster supplement; it has the EFSA Article 13.1 claim for normal nervous-system function. Where oral melatonin is lawful elsewhere, melatonin + magnesium is a common pairing. In the UK retail context, magnesium glycinate is one of the lawful alternatives Camden signposts.
Magnesium contributes to normal nervous-system function via NMDA receptor modulation and other neuromuscular signalling pathways. Melatonin acts on MT1/MT2 receptors. Mechanisms are separate; narrative additive logic for evening dosing. Pivotal-trial evidence for the combination is limited.
Evidence: Both ingredients have small sleep-context trial bodies of evidence. Combination has not been the subject of pivotal UK trials.
Doses studied: Where lawful in the destination jurisdiction: melatonin 0.5–1 mg + magnesium glycinate 200–400 mg evening dose. Not a UK retail context.
Valerian (Valeriana officinalis)
Limited evidenceValerian has UK MHRA Traditional Herbal Registration (THR) for sleep difficulty — a UK-lawful sleep-cluster alternative to oral melatonin. The two work via different mechanisms and the THR registration is the UK retail framing for valerian.
Valerian has GABA-A receptor modulation activity (valerenic acid and valeranone are the principal characterised actives). Mechanism is non-overlapping with melatonin''s MT1/MT2 receptor mechanism. In jurisdictions where oral melatonin is permitted, the combination is sometimes used; UK retail context defaults to valerian alone under THR registration.
Evidence: Valerian has Cochrane-reviewed mixed evidence for sleep latency and quality. Combination with melatonin has not been the subject of pivotal trials.
Doses studied: UK retail: valerian 300–600 mg evening dose under THR. Combination with imported melatonin is not a UK retail context.