Medscript

Melatonin: uses, dosage and side effects

Melatonin is a hormone produced by the pineal gland that tells the body it is night. As a medicine it is used for sleep problems, and in Ireland the licensed melatonin products are prescription-only. This page sets out what melatonin is used for, how the licensed products are taken, the side effects described in the product information, and what happens when an existing course needs a repeat prescription.

What melatonin is used for

Melatonin is used for sleep problems, mainly difficulty falling asleep and poor sleep quality. The best known licensed form in Europe is a prolonged-release 2 mg tablet authorised for the short-term treatment of primary insomnia in adults aged 55 and over. A separate prolonged-release product is authorised for insomnia in children and adolescents with autism spectrum disorder or Smith-Magenis syndrome, where sleep hygiene measures on their own have not worked. Doctors also use melatonin outside those licensed indications, for example around long-haul travel or shift work, and that use is a clinical judgement made case by case rather than something covered by the marketing authorisation. Melatonin does not sedate the way a hypnotic does. It shifts the timing signal for sleep, so it is normally taken at a fixed hour each evening and judged over a run of nights rather than after a single one.

Side effects of melatonin

The side effects listed in the product information for melatonin include headache, dizziness, daytime sleepiness, nausea, dry mouth and abdominal pain. Some people report vivid dreams, restlessness, irritability or a low mood while taking it. The frequency category attached to each reaction is printed in the leaflet supplied with your pack, and it differs between the adult and the paediatric products, so read the leaflet for the exact preparation you were given rather than a general list. Because daytime sleepiness is possible, do not drive or use machinery until you know how melatonin affects you. Stop taking it and seek medical help straight away if you develop a rash, swelling of the face, lips or throat, or difficulty breathing, as these can indicate an allergic reaction. Suspected side effects can be reported to the HPRA through its national reporting system.

Dosage and how to take melatonin

The licensed adult prolonged-release tablet is taken once daily, one to two hours before bedtime and after food. The tablet is swallowed whole; crushing or chewing it destroys the prolonged-release structure and changes how the dose is delivered. Paediatric prolonged-release products are dosed by the prescribing specialist and are also given before bedtime. The prescriber sets the treatment period, and the licensed adult indication is short-term rather than open-ended, so treatment is meant to be reviewed rather than continued indefinitely without a look at whether it is still helping. Take it at the same hour every evening; an irregular schedule works against the whole point of the medicine. If you miss a dose, skip it and take the next one at the usual time. Never double up to catch up. Do not change your dose without speaking to the prescriber.

Is melatonin prescription-only in Ireland?

Yes. Melatonin is a prescription-only medicine in Ireland and a pharmacy supplies it against a valid prescription. This surprises many people who have travelled, because in several countries outside the European Union the same substance sits on an open shelf as a food supplement. The difference is regulatory rather than pharmacological: in Ireland melatonin products are authorised as medicines, so an authorised prescriber has to judge whether the treatment is suitable first. Supplement-grade melatonin brought in from abroad is not a substitute, because the strength, the release profile and the quality standards of a supplement are not those of an authorised medicine. If sleep problems are new, persistent, or come with low mood, snoring with pauses in breathing, or daytime exhaustion, the right first step is an assessment by your own GP rather than a medicine.

Continuing melatonin and getting a repeat prescription

If a GP or a specialist in Ireland has already started you on melatonin, the treatment is working, and your supply is running low, you can ask a doctor to review a continuation of that same treatment through our online medical questionnaire. There is no video consultation and no phone appointment: you complete a structured medical questionnaire, a doctor reviews it, and if continuation is appropriate you receive a prescription document by email as a PDF laid out to the Annex of Directive 2012/52/EU. You bring it to any pharmacy with photo identification. There is no PIN code and no national identity number on it. The assessment for a repeat prescription costs 19,90 €. The fee covers the medical assessment, not the issuing of a document. If the doctor declines on medical or legal grounds, the fee is refunded. If the doctor asks you for documentation, you have at least 7 days to provide it and we will remind you before the deadline; if the consultation cannot be completed, we refund the full amount. Two limits matter here. First, this route is for continuing an existing treatment, not for starting melatonin; a first course needs a doctor who can examine you and take a full sleep history. Second, the doctor may decide that continuation is not appropriate, for example where the reason for treatment has changed.

Cost and reimbursement in Ireland

What you pay at the counter for melatonin depends on the product, the pack size and which HSE arrangement covers you. If you hold a medical card, prescription items are supplied under the General Medical Services scheme with the item charge that applies at the time. If you do not, the Drugs Payment Scheme caps what a person or family pays for approved prescribed items in a calendar month, and you register for it through the HSE rather than through a pharmacy. Melatonin preparations differ in price, so ask your pharmacist what your specific prescription will cost before you commit to a long course. The current charges and thresholds are published by the HSE and change from time to time, so check the HSE pages rather than relying on a figure quoted on any commercial website, including this one.

Interactions and alcohol

Melatonin is broken down mainly by liver enzymes in the CYP1A family, so anything that blocks or induces those enzymes changes the amount circulating in your blood. Fluvoxamine is the clearest example of a medicine that raises melatonin levels substantially, and the combination is avoided. Ciprofloxacin, oestrogens including some hormonal contraceptives, and smoking status can all shift melatonin levels in one direction or the other. Sedatives, benzodiazepines and other medicines that cause drowsiness add to melatonin's effect on alertness. Tell the prescriber and your pharmacist about every medicine you take, including anything bought over the counter and any herbal product. Alcohol is best avoided while taking melatonin: it disrupts sleep architecture in its own right, which works against the treatment, and it adds to the sedative effect.

Who should not take melatonin

Melatonin is not suitable for anyone who has had an allergic reaction to melatonin or to any of the excipients listed in the leaflet. Caution is needed in autoimmune conditions, where experience is limited, and in significant liver or kidney impairment, because clearance of the substance is altered. It is not a treatment for insomnia caused by an untreated condition: obstructive sleep apnoea, restless legs, chronic pain, an overactive thyroid, depression and a harmful drinking pattern all need to be addressed in their own right, and a sleep medicine layered on top can mask them. People who drive professionally or operate machinery should discuss timing with the prescriber. If you take treatment for epilepsy or a blood thinner, flag it before starting, as the prescriber may want closer monitoring.

Generic and brand names

Melatonin is the international non-proprietary name of the active substance, and it is the name a pharmacist anywhere in the European Union recognises. In Ireland it is supplied under brand names as well as under the substance name; prolonged-release 2 mg tablets for adults and a prolonged-release preparation for children are the forms seen most often. Immediate-release and prolonged-release melatonin do not behave the same way, so a prescription should be read as the exact preparation rather than as the substance alone, and a switch between preparations is a prescribing decision rather than a substitution made at the counter. If your pack looks different from the previous one, check with the pharmacist that the release profile and strength match your prescription before you take the first dose. On a cross-border prescription the substance is written by its international name, which is what makes it readable in an Irish pharmacy.

Pregnancy and breastfeeding

Melatonin is not recommended during pregnancy or while breastfeeding. There is not enough clinical data on its use in pregnancy to establish safety, and melatonin passes into human breast milk, so the licensed products advise against use in both situations. Women who could become pregnant should discuss this with the prescriber before starting, and anyone who becomes pregnant while taking melatonin should contact their GP or maternity team rather than simply continuing. Sleep problems in pregnancy are common and often have a physical cause that can be addressed directly, so a review with a midwife or GP is more useful than a medicine in many cases. If you are breastfeeding and were prescribed melatonin before the birth, do not restart it on your own initiative; ask the doctor who knows your case.

Patient information leaflet

Every pack of melatonin dispensed in Ireland contains the patient information leaflet for that exact product, and it is the authoritative document for your treatment. It lists the licensed indication, the strengths, the full set of side effects with their frequency categories, the interactions, and what to do about a missed dose. The same leaflets and the fuller summary of product characteristics are published online by the HPRA, which authorises and monitors medicines in Ireland, and on the Irish medicines information portal. Read the leaflet for the preparation you were actually given, because the adult prolonged-release tablet and the paediatric product carry different information. Keep the leaflet for as long as you have the pack. If anything in it contradicts what you read here, the leaflet and your prescriber win.

About this page

This page was written by the medical team at MEDINOW Sp. z o.o. and reviewed by lek. Damian Wojno, a doctor registered in Poland, PWZ no. 3211301. He holds a Polish licence to practise; he is not on the register of the Irish Medical Council, and this page does not suggest otherwise. Content verified on 29 August 2026 against the summary of product characteristics and the patient information leaflet published for the Irish market, and against public guidance from the HPRA and the HSE. This page is information, not advice for your particular case, and it is not an advertisement for a prescription medicine. Nothing here replaces an assessment by your own GP or a hospital clinician. If you are unwell and need urgent help, contact your GP, an out-of-hours service, or call 112 or 999.

Is melatonin prescription-only in Ireland?

Yes. Melatonin products are authorised as medicines in Ireland and a pharmacy supplies them only against a valid prescription. The fact that it is sold as a food supplement in some countries outside the European Union does not change the position here.

How long does melatonin take to work?

The licensed adult tablet is taken one to two hours before bedtime because it works by shifting the body's night signal rather than by sedating you. Judge it over a run of nights at a fixed hour, not after a single night. If there is no benefit by the end of the period your prescriber set, go back to them rather than raising the dose yourself.

What are the common side effects of melatonin?

Headache, dizziness, daytime sleepiness, nausea, dry mouth and abdominal pain are among the reactions listed in the product information, and vivid dreams or irritability are also reported. The frequency of each is in the leaflet for your pack. Stop taking it and seek help if you develop a rash, facial swelling or difficulty breathing.

Can I drink alcohol while taking melatonin?

Alcohol is best avoided. It disrupts sleep quality on its own, which undermines the reason for taking melatonin, and it adds to the drowsiness the medicine can cause. If you do drink, do not drive and do not operate machinery.

How do I get a repeat prescription for melatonin?

If an Irish GP or specialist already started you on melatonin and it is working, you can ask a doctor to review a continuation through our online medical questionnaire, for 19,90 €. The fee covers the medical consultation, not the issuing of a document - the doctor decides after reviewing your form. If the doctor declines for medical or legal reasons, we refund the fee in full. If the doctor asks you for documentation, you have at least 7 days to provide it, and we will remind you before the deadline; if the consultation cannot be completed, we also refund the full amount. A first course of melatonin needs an in-person assessment instead.