What it is

Melatonin is the same substance your body makes at night to set your body clock. Your capsule is the slow-release form, so it releases melatonin gradually through the night. Your doctor sets your dose.

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How to take it

• Take it after your evening meal, 1 to 2 hours before bed. Food slows the absorption, so your level is highest while you sleep.¹
• Swallow the capsule whole. Do not open, crush or chew it. This keeps the slow release working through the night.¹
• Take the number of capsules written on your label. Your doctor changes your dose by changing the number of whole capsules, so there is no need to split anything.
• If you have diabetes or insulin resistance, take it at least 2 hours after your evening meal. Melatonin taken close to a meal may make blood sugar rise more.²
• Do not drive or use machines after taking it. Melatonin can make you drowsy.¹
• If you feel sleepy or heavy-headed in the morning, tell us. Your doctor may ask you to take it earlier in the evening.

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If you miss a dose

Skip that night. Do not take it later in the night, and do not take two doses the next night. A late dose would still be working in the morning and could make you drowsy.

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If you stop

There is no withdrawal. In studies, sleep slowly returned to how it was before, without rebound insomnia.¹ Melatonin leaves your body within about a day,¹ so nothing builds up.

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Please stop

• Any other melatonin product. You cannot know how much melatonin it really contains,³ and taking it with your capsule adds to your dose.

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Tell us if you take

None of these automatically means you cannot take melatonin. Some medicines change how your body handles melatonin, so knowing what you take helps us look after you more closely.

• Fluvoxamine, an antidepressant. It raises melatonin many times over, so we do not give the two together.¹ Your own doctor can advise on other ways to help your sleep.
• Quinolone antibiotics, cimetidine (a stomach medicine), estrogen (the pill or hormone replacement), or psoralen (5- or 8-methoxypsoralen). These slow down how your liver clears melatonin, so your level can be higher.¹ You can still take melatonin. We simply ask about side effects at every visit.
• Carbamazepine (a seizure medicine), rifampicin (a tuberculosis medicine), or smoking. These speed up how your liver clears melatonin, so it may work less well.¹
• Sleeping pills, such as zolpidem, zopiclone or benzodiazepines. Melatonin adds to their drowsiness, and taken with zolpidem it affected attention, memory and balance.¹ We need to know so that we can plan safely.
• Medicines that suppress the immune system. We do not give melatonin in this case, because there is no information on its safety.
• Any new medicine you start while taking melatonin, so we can check that the two work well together.

Please also avoid alcohol while you take melatonin. Alcohol weakens its effect.¹

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Contact us if you notice

Side effects are uncommon. In studies of the licensed slow-release melatonin medicine, nightmares and unusual dreams affected fewer than 1 in 100 people.¹ We tell you about these so that you know what to look out for, as part of good care.

• Morning sleepiness or a heavy head, nightmares, dreams so vivid it is hard to tell them from reality, waking too early with a pounding heart or sweating, or sleeping much longer than usual. These can be signs that the dose or the timing is not right for you. Usually taking it earlier, or a lower dose, solves it.
• Headaches, or feeling weak or tired when you stand up. Melatonin can lower the activity of cortisol, your stress hormone.⁴ We will ask you to pause melatonin and check your cortisol.
• Low mood, or mood that gets worse.¹ We will ask you to pause melatonin while we check.
• A rash, or swelling of the mouth or tongue.¹ Stop the capsules and contact us. Go to a hospital the same day if you have trouble breathing or the swelling is severe.
• If you become pregnant, stop the capsules and contact us.

These signs often have other causes. We will check you to find out.

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How to store it

• Keep it in its original bottle, away from light and moisture.
• Store it below 25°C, in a cool, dry place.
• Keep it out of the sight and reach of children.

Medically reviewed by Dr. Chontirot, MD · Medical licence no. 36583 · Last reviewed: 31 October 2026

References

1. Flynn Pharma Ltd. Circadin 2 mg Prolonged-release Tablets — Summary of Product Characteristics. emc, UK; updated 2025.

2. Rubio-Sastre P, Scheer FA, Gómez-Abellán P, et al. Acute melatonin administration in humans impairs glucose tolerance in both the morning and evening. Sleep. 2014;37(10):1715–1719.

3. Erland LA, Saxena PK. Melatonin natural health products and supplements: presence of serotonin and significant variability of melatonin content. J Clin Sleep Med. 2017;13(2):275–281.

4. Arendt J, Aulinas A. Physiology of the Pineal Gland and Melatonin. In: Feingold KR, Adler RA, Ahmed SF, et al., editors. Endotext. MDText.com; updated 2022.

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