Melatonin can cause drowsiness, interact with medications and is not suitable for everyone. Short trials are fairly reassuring regarding serious adverse events, but they do not prove that daily use for years is safe. The smart move is to check your circumstances before buying another bottle.
If you experience chest pain, significant difficulty breathing, loss of consciousness or a severe allergic reaction, seek urgent help: in France, call 15 or 112. This guide is for safety checks, not remote emergency triage.
Documentation and French regulatory context checked: October 16, 2026. This text has not been reviewed by a healthcare professional. It must not be presented as “medically reviewed.”
Known side effects and the limits of frequency data
Melatonin is a hormone that, among other things, sends a timing signal to the body. A naturally produced substance can have pharmacological effects when swallowed. The word “natural” describes an origin or a resemblance, not a safety certificate.
The 2019 systematic review by Besag and colleagues included 37 randomized placebo-controlled trials in sleep disorders. Most lasted four weeks or less. Reported effects mainly included daytime drowsiness, headaches and dizziness. Few clinically important events were described, with limitations in study quality and adverse event collection.
This supports a measured conclusion: the events observed in these trials were generally mild. It does not allow you to calculate your personal risk or rule out a rare event in someone taking several medications.
A report does not give you a risk rate
In its 2018 opinion, Anses analyzed 90 reports received up to May 2017 concerning supplements containing melatonin. Only 19 were sufficiently documented for a causality assessment. That does not mean “19 proven cases.”
These figures are historical, not an up-to-date overview of all users. Without precise information on the number of people exposed, doses, durations and unreported cases, no frequency can be inferred. Conversely, possible underreporting does not justify inventing the actual number of incidents.
When reading a safety figure, distinguish three levels:
- Report : an event occurred after use and warrants investigation.
- Observed frequency : a study documents events in a defined population over a defined period.
- Causal link : a body of evidence allows the event to be attributed to the product, with an explicit degree of certainty.
This distinction avoids two opposite mistakes: dismissing every signal or treating every sequence of events as causation.
Groups who should avoid self-medication
French recommendations go beyond “ask for advice if you’re unsure.” The 2018 Anses opinion distinguishes situations in which supplements should be avoided from those requiring medical advice.
The Agency advises against these supplements in the following situations:
- Pregnancy and breastfeeding.
- Childhood and adolescence.
- Inflammatory or autoimmune disease.
- Activities requiring sustained alertness, where drowsiness could compromise safety.
Medical advice is needed before use if you have epilepsy, asthma, mood, behavioral or personality disorders, or if you take medication. The December 2024 Anses opinion reiterates these groups and the many combinations that need checking.
Liver or kidney disease must also be mentioned to the prescriber. The Circadin Summary of Product Characteristics includes specific precautions for these situations. An over-the-counter box does not make your medical circumstances irrelevant.
These precautions concern buying a supplement on your own. They do not mean that all specialist prescribing of melatonin is prohibited, particularly in pediatrics. Do not apply a treatment prescribed for one child to all the children in the family.
Medications and combinations to check
There are two main types of interactions: a medication can alter melatonin exposure, or several substances can have additive effects, particularly on alertness. Taking them a few hours apart does not necessarily prevent these mechanisms.
The European Summary of Product Characteristics (SmPC) for Circadin and Anses opinions provide practical guidance. This table helps you prepare for a discussion, not change a prescription:
| Treatment or combination | Point to watch | What to do before adding a supplement |
|---|---|---|
| Fluvoxamine | Substantial increase in melatonin exposure | Avoid this combination according to the SmPC; contact the prescriber |
| Benzodiazepines, zolpidem, zopiclone | Increased sedation and impairment of attention or coordination | Do not add melatonin without medical advice |
| Oestrogens, including contraception or hormone therapy | Melatonin exposure may increase | Have the combination checked, without stopping contraception |
| Certain antibiotics, carbamazepine | Exposure may increase or decrease depending on the medication | Give the pharmacist and doctor the exact name |
| Anticoagulants, antiplatelets, blood pressure medications | Possible interactions reported by Anses | Medical review; do not make changes on your own |
| Alcohol and other sleep products | Combination to avoid; benefits and alertness are less predictable | Do not combine them to boost the effect |
This is not an exhaustive list. Also disclose over-the-counter medications and products you take occasionally. A “sleep” product may contain several active ingredients, each with its own precautions.
Anses noted in 2024 the value of simple formulations and recommended avoiding the combined use of supplements containing melatonin. Count tablets, sprays, gummies and any medication together. Two different packages do not mean two independent risk categories.
Daily use: what we know and the long-term unknowns
Studies lasting longer than a few weeks do exist. So the problem is not a complete lack of data. The 2022 review by Besag and Vasey, covering prospective studies lasting at least six months, reports few significant events but highlights the lack of robust, double-blind, placebo-controlled trials over these durations.
Several limitations prevent this finding from becoming a guarantee for years of use: study populations are selected, formulations differ, and some rare effects require very large samples to detect. Good tolerability for one month is useful information, not lifetime insurance.
For a medication, daily use may be planned within a specific framework. Prolonged-release Circadin is indicated for short-term use in certain adults aged 55 or over, for up to thirteen weeks according to its SmPC. That does not validate thirteen weeks of any supplement, at any dose, in every population. The prolonged-release melatonin · FR guide explains this distinction between formulation, indication and duration.
If you have been taking it every night for several months, prepare for a reassessment: the original reason, observable benefits, drowsiness, new medications and the cause of your sleep problems. There is no universal day when melatonin suddenly becomes dangerous. Still, automatic renewals are a poor approach to follow-up.
What do we know about heart risks?
A presentation at the AHA in 2025 examined the records of 130,828 adults with insomnia. Documented use for at least one year was associated with more heart failure diagnoses over five years: 4.6% versus 2.7% in the comparison group. The observed difference is 1.9 percentage points, not a causal risk attributable to the product.
The study is observational. Non-prescription use may have been missing from the records, and insomnia severity and other factors were incompletely documented. Differences between groups may therefore remain despite matching. The data reviewed come from the conference presentation and the institutional press release, not a randomised trial demonstrating causality.
I would not interpret this signal as “melatonin damages the heart”, nor reassuring short-term trials as “no heart risk”. It warrants a discussion about prolonged use, without requiring you to stop a prescribed treatment on your own. If you have cardiovascular disease or take blood pressure medication, bring this information to your appointment.
French framework: document review dated 16 October 2026
The 2018 Anses opinion describes supplements marketed in France at less than 2 mg per day. The opinion dated 24 December 2024 discusses the French benchmark of 1.9 mg and reiterates safety uncertainties even below 2 mg. This is an expert assessment and discussion of the regulatory framework, not proof that a dose is safe.
For a medication, the SmPC specifies an indication, a formulation, precautions and a duration. Do not confuse permission to market a supplement, a claim about falling asleep and marketing authorisation for a medication. Rules also differ between countries: a product bought abroad does not define the conditions that apply in France.
The dated review covers the institutional documents cited, not testing of a batch or brand. Check the exact status of the product you use with your pharmacist. This guide recommends no brands and contains no affiliate links.
Drowsiness, stopping use and seeking medical advice
If you are drowsy the next day
Do not drive or use machinery while your alertness is impaired. Do not try to mask this effect with more coffee so you can continue a dangerous activity. If you started the supplement without a prescription, stop taking it and seek advice before taking it again.
Note the time, dose, formulation and other substances consumed. For a prescribed medication, contact the prescriber or pharmacist to review what to do next. Do not compensate by randomly increasing the dose or changing when you take it.
If a symptom appears after taking it
A new symptom is not automatically caused by melatonin. It should nevertheless be described and assessed, especially if it persists or bothers you. Keep the packaging, ingredient list and batch number. The NCCIH highlights, among other things, the risks of drowsiness, allergy and interactions.
A severe allergic reaction, difficulty breathing, chest pain or loss of consciousness requires urgent help. In the event of a large accidental ingestion or ingestion by a child, contact a poison control centre or emergency services immediately, depending on the symptoms, without waiting for drowsiness to appear.
Then report the event to a healthcare professional, who can contribute to nutrivigilance monitoring. Do not deliberately take the product again to “check” whether it causes the same reaction.
If the sleep problem persists
A prolonged daily need may conceal an untreated cause: a sleep-related breathing disorder, an unsuitable schedule, pain, a mood disorder or another medical problem. The 2023 European guidelines place cognitive behavioural therapy for insomnia as the first-line treatment for chronic insomnia. The right decision is not always to find another capsule.
The checklist for your doctor or pharmacist
Download the consultation checklist as a PDF or open the printable HTML version. The boxes are blank: they help you prepare for a discussion, without giving you an automatic green light.
Gather the following information before your appointment:
- Product name, a photo of the label, immediate- or prolonged-release formulation and total amount per day.
- Start date, frequency, time taken and original reason.
- All medications and supplements, with doses and timing, including occasional use.
- Pregnancy, breastfeeding, chronic conditions and activities requiring sustained alertness.
- Perceived benefit, new symptoms and their timeline.
- Decision discussed: continue, pause or change approach, with a reassessment date.
This preparation avoids a consultation based solely on “I’m taking something natural to sleep.” The exact name and timeline give the healthcare professional the information needed to assess the combination.
The Verdict
Main sources
The Anses opinions and the Summary of Product Characteristics were consulted in their official institutional documents. The 2019 and 2022 reviews were checked using their indexed abstracts. The cardiac signal is presented according to the status of the data consulted: an observational conference presentation:
