Melatonin: effects in the body

Melatonin is a hormone that controls the sleep-wake cycle. It is also known as the circadian rhythm.

The sleep hormone is released naturally in the body when light conditions change:

If the eyes perceive darkness, a signal is sent to the pineal gland. The pineal gland, also known medically as the glandula pinealis, is located in the brain. Melatonin is synthesised from serotonin in the pineal gland. The pineal gland is an endocrine gland. It therefore releases its product, melatonin, directly into the bloodstream.

The sleep hormone therefore enters the bloodstream and signals to the body that it is time to relax and prepare for sleep. The melatonin level in the blood rises and remains high during the night. It drops again in the early hours of the morning when daylight increases. This is because daylight inhibits the production of the sleep hormone.

The hormone therefore controls the fact that people are awake during the day and become tired in the evening. It regulates the circadian rhythm [2,3]

Melatonin not only influences the sleep-wake cycle, but also plays a role in regulating body temperature, blood pressure [8] and hormone levels [2]. There is also evidence that the hormone has antioxidant properties [5-7] and can support the immune system [4]. Its functions therefore go far beyond sleep.

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Melatonin for falling asleep?

The effectiveness of melatonin is well documented in research. This is particularly true for short-term use and with regard to certain applications such as jet lag and shift work.

In the case of jet lag, for example, the sleep-wake rhythm is disturbed because the person is in a different time zone for a short period of time. For shift workers, the sleep rhythm changes due to working hours.

Studies show that melatonin can help to shorten the time it takes to fall asleep and improve sleep quality in the case of jet lag and shift work. This is particularly true for people with insomnia. Melatonin has also been shown to be helpful for older people whose melatonin production decreases with age [9].

However, melatonin alone is not a miracle cure for sleep problems. It is important to combine the intake of sleep-inducing supplements with healthy sleep habits. This includes maintaining a regular bedtime, avoiding caffeine and heavy meals before bed and creating a dark, quiet sleeping environment.

Light sources, especially blue light from screens, can significantly impair melatonin production. It is therefore recommended to stop using electronic devices with blue light one hour before going to bed in order to support the body's own melatonin production.

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Medication and dietary supplements

A large number of melatonin medications are currently (2024) authorised in Germany. It is also available in over-the-counter food supplements.

Melatonin is used medically for the short-term treatment of primary insomnia, which is characterised by poor sleep quality. The usually recommended dose of melatonin is 2 mg per day [1]. It should be taken one to two hours before bedtime, after the last meal. To avoid a melatonin overdose, the recommended intake should not be exceeded.

Over-the-counter supplements containing the sleep hormone or a precursor of the hormone are available in various forms. These include tablets, capsules, lozenges and sprays. As the approval process for over-the-counter supplements is not standardised and not very well regulated, the dosage, composition and quality of the supplements can vary greatly [10].

In principle, good quality should be ensured for over-the-counter supplements, which should ideally be externally standardised or accredited. The manufacturer's recommended daily dose should also not be exceeded.

If sleep disorders are due to a medical condition, supplementation should be discussed with the treating doctor in order to use controlled, authorised medication and avoid interactions with other medications.

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Side effects and risks

Melatonin is generally considered safe for healthy people. Nevertheless, sleep-promoting preparations can be associated with side effects.

Melatonin side effects that have been commonly described include

• Mood swings
• Aggressiveness, irritability
• Somnolence, sudden sleep attacks
• headaches
• Sinusitis (inflammation of the paranasal sinuses)
• Exhaustion, tiredness in the morning

The effects of long-term use of melatonin preparations have not yet been fully researched. Researchers suspect that long-term use of melatonin could impair the body's natural production. It is therefore recommended that supplements should only be taken temporarily. Higher doses in particular should only be taken in consultation with a doctor.

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Interactions

If sleep disorders are caused by illnesses, the medication for the underlying illness should first be checked for interactions with melatonin preparations.

Melatonin is mainly metabolised by so-called CYP1A enzymes. Therefore, interactions with drugs or substances that also act on CYP1A enzymes are possible [1].

Caution is therefore advised, among other things, in the treatment of

• Depression with the antidepressant fluvoxamine
• cutaneous T-cell lymphoma with 5- or 8-methoxypsoralen
• certain skin diseases such as psoriasis vulgaris (psoriasis) with 5- or 8-methoxypsoralen
• inflammation of the oesophagus, gastric ulcers or Zollinger-Ellison syndrome with the CYP2D inhibitor cimetidine
• epileptic and non-epileptic seizures with CYP1A2 inducers such as carbamazepine
• Nerve pain due to trigeminal neuralgia or diabetic neuropathy with CYP1A2 inducers such as carbamazepine
• Mycobacteria with CYP1A2 inducers such as rifampicin

Interactions are also known with oestrogens, which are used for contraception or hormone replacement therapy, for example.

Caution is also advised for smokers, as there are interactions.

Melatonin should not be taken together with:

• Alcohol, as this reduces the effect of melatonin on sleep.
• Benzodiazepines and non-benzodiazepine hypnotics such as zolpidem or zopiclone, as melatonin can increase the sedative properties.
• Please note that the above list is not exhaustive. Check the package leaflet of your medication to see if there are any interactions with melatonin. The Yellow List also provides an overview. In general, you can always consult your doctor or pharmacist to check for possible interactions.