A growing number of customers walk into UK pharmacies asking for melatonin by name, often after reading US online forums or buying it on a trip abroad. Others arrive asking for 5-HTP, marketed as a "natural" sleep aid. These products sit in very different regulatory categories in the UK, and confusing the two is one of the most common counter errors.
Melatonin in the UK: prescription only
Melatonin is a prescription-only medicine (POM) in the UK, whether branded (Slenyto, Circadin, Syncrodin) or generic. It cannot be supplied over the counter. This is different from the United States, where melatonin is sold as a dietary supplement on supermarket shelves, and from much of continental Europe, where availability varies by country.
The BNF lists the licensed indications as short-term treatment of primary insomnia in adults aged 55 and over (Circadin 2 mg prolonged release), insomnia in children and adolescents aged 2–18 with autism spectrum disorder and/or Smith–Magenis syndrome (Slenyto), and jet lag (various). In practice, prescribers also use it off-label for delayed sleep phase disorder and for insomnia in older adults who have not responded to sleep hygiene.
The counter conversation, therefore, is often about what melatonin is and how to access it, not a direct supply. Customers returning from the US or buying online should be advised that imported melatonin is unlicensed, may be variable in strength (US studies have found labelled doses wrong by a factor of 4 in some products), and that any discussion of dose and duration belongs with a prescriber.
5-HTP: food supplement with real pharmacology
5-Hydroxytryptophan is the immediate precursor of serotonin and is sold in the UK as a food supplement, typically at 50 mg or 100 mg per capsule, from the amino acid derived from Griffonia simplicifolia seeds. It is not a medicine and carries no approved health claim for sleep.
The evidence base for 5-HTP in insomnia is thin. A small number of trials have reported improvements in subjective sleep quality, typically in combination with GABA or other agents, at doses of 100–300 mg at night. Effect sizes are modest and studies are mostly under 4 weeks.
Safety is the bigger issue. 5-HTP raises serotonergic activity and has a theoretical — and occasionally reported — risk of serotonin syndrome when combined with:
- SSRIs and SNRIs
- Tricyclic antidepressants
- Monoamine oxidase inhibitors (including isocarboxazid, moclobemide and the antibiotic linezolid)
- Tramadol, pethidine, fentanyl
- Triptans
- St John's Wort
This makes the medicines history essential before any supply. A customer on sertraline who takes 200 mg of 5-HTP at bedtime is exposing themselves to avoidable risk.
The NICE position on insomnia
NICE's clinical knowledge summary on insomnia recommends stepped care, starting with sleep hygiene and cognitive behavioural therapy for insomnia (CBT-I). Short courses of Z-drugs or short-acting benzodiazepines are options when non-drug measures fail. Melatonin is a second-line option in specific groups. Antihistamines such as diphenhydramine or promethazine (available OTC) are mentioned but with limited evidence for efficacy and significant next-day sedation, particularly in older adults.
Notably, NICE does not recommend 5-HTP, valerian or other supplements for insomnia. This is a useful counterweight to the marketing a customer may have seen online.
What the pharmacy team can do
Three practical responses tend to land well with customers asking for melatonin or 5-HTP.
First, screen for red flags. Insomnia lasting more than three months, significant daytime impairment, symptoms of sleep apnoea (loud snoring, witnessed apnoeas, unrefreshing sleep despite adequate duration), restless legs, depression or new medicines should route to GP or Pharmacy First where in scope.
Second, reinforce sleep hygiene and CBT-I. NHS-backed digital CBT-I is available via Sleepio in several ICBs and free access is widening. Signposting is often more useful than any supply.
Third, for customers who are insistent on an OTC option, the licensed antihistamines (promethazine hydrochloride 20–25 mg at night for short-term use in adults) are the evidence-based choice available over the counter. Caveat the known next-day drowsiness, anticholinergic burden in older adults and interactions with alcohol.
Red flags for referral
| Situation | Action |
|---|---|
| Insomnia > 3 months | Refer to GP |
| Suspected OSA | Refer |
| Low mood, anxiety, suicidal thoughts | Refer urgently |
| On SSRI/SNRI/TCA/MAOI/tramadol/triptan | Do not supply 5-HTP |
| Pregnant or breastfeeding | Refer, supplements not advised |
| Child under 18 | Refer; OTC options limited |
| Shift worker | Sleep hygiene, consider GP for melatonin |
Where this sits in the UK pharmacy picture
Sleep is one of the most common reasons for self-care consultations in community pharmacy. PharmSee's pharmacy directory lists the UK contractor base customers rely on for this kind of advice, and our pharmacy jobs listings show that clinical roles increasingly require confident management of chronic self-care topics like insomnia alongside the medicines pathway.
Caveats
This piece summarises the BNF, NICE CKS, MHRA and NHS positions as of April 2026. Prescription-only status can change — melatonin has been periodically reviewed — so always check the latest BNF entry before counselling. Nothing here replaces individual prescriber judgement, and any customer with a complex medicines list needs a full medicines reconciliation before supplements are added.