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Melatonin: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 30, 2023.

1. How it works

  • Melatonin is a supplement that may be used to aid sleep and help decrease jet lag. It is also reported to have a range of other actions in the body.
  • Melatonin is a natural hormone produced mainly by the pineal gland that our body secretes in response to darkness to help maintain our sleep-wake cycle. Environmental light inhibits the secretion of melatonin, and darkness stimulates the secretion of melatonin. Secretion of melatonin in humans starts around 9 pm and peaks between 2 and 4 am; with the duration of melatonin production varying from season to season.
  • Natural melatonin is synthesized from the amino acid tryptophan and released into the blood and cerebrospinal fluid where it works by acting on receptors in the brain and other areas of the body. Most melatonin that is available as a supplement is a synthetic version of naturally occurring melatonin.
  • Melatonin taken as a supplement mimics the effects of naturally occurring melatonin. It may be called a hormone, a supplement, a miscellaneous hypnotic, or a nutraceutical.

2. Upsides

  • Melatonin is classed as a supplement which means it is available without a prescription from pharmacies, nutrition stores, and other retail outlets.
  • Melatonin may be used to treat jet lag, sleep disorders in the blind, shift-work sleep disorders, and general insomnia. It is an antioxidant and is thought to have numerous other properties (such as boosting the immune system and treating headaches).
  • May improve sleep problems in children with autism, Asperger syndrome, or pervasive developmental disorder.
  • May be used for several other conditions (such as fibromyalgia).
  • The majority of trials have investigated the use of melatonin for jet lag. A review found melatonin to be very effective at decreasing jet lag from eastward flights crossing five or more time zones. A dosage of 0.5 mg/day immediately before bedtime once at the destination appears just as effective as a dosage of 5 mg/day; however, onset and quality of sleep are better with the 5mg dosage. The 2mg slow-release dose appears ineffective; suggesting that a short-lived, high-peak concentration of melatonin works better.
  • Melatonin appears more effective the more time zones that are crossed, and less effective for westward flights.
  • Occasional short-term use appears safe.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Dizziness, drowsiness, bed-wetting, headache, nausea, and excessive daytime sedation are the most common side effects.
  • Melatonin may cause drowsiness that persists and affects a person's ability to drive or operate machinery the next day.
  • Not FDA approved for any use.
  • May not be suitable for some people including those with epilepsy, diabetes, autoimmune diseases, depression, bleeding or clotting disorders, or taking blood thinners such as warfarin. Caffeine and fluvoxamine may elevate plasma concentrations of melatonin. Melatonin may decrease plasma concentrations of nifedipine.
  • If melatonin is not taken at the right time of day it may cause drowsiness and delay adaption to local time.
  • Some melatonin supplements use naturally occurring melatonin derived from animal pineal tissue. Their use is to be discouraged because of the risk of contamination or viral transmission.
  • High doses of melatonin may affect ovulation, making it difficult for a woman to get pregnant.
  • Melatonin may not work for everyone.
  • Should not be given to children without medical advice.
  • Dosages over 5mg appear no more effective than lower dosages and are associated with more side effects such as headache, next-day dizziness, or vivid dreams. Side effects may be worse in older adults.
  • Should not be used by women who are pregnant and medical advice should be sought before using it while breastfeeding.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, see product information.

4. Bottom Line

  • Supplemental melatonin is very effective at reducing symptoms of jet lag, particularly that brought about by eastward travel across five or more time zones. Melatonin may also be used to treat sleep disorders and general insomnia. It is an antioxidant and may also help support the immune system, although studies are limited supporting its use for other indications.

5. Tips

  • For jet lag, take melatonin as close to bedtime at your destination as possible (10 pm to midnight). Take short-acting rather than slow-release melatonin for jet lag.
  • For westbound travel, melatonin should be taken for four nights once in the new time zone. For eastbound travel, one dose of melatonin should be taken before the flight in the early evening, followed by once at night for four nights after arrival.
  • For sleep disorders, melatonin 5mg should be taken three to four hours before a defined, set, bedtime. people who have difficulty maintaining sleep should consider high-dose, repeated low-dose, or controlled-release melatonin.
  • Buy melatonin from a reputable brand with good quality control measures.
  • Do not drive or operate machinery if you feel sleepy with melatonin or the sleepiness persists the next day.
  • Caffeine (contained in coffee and cola) may increase the effects of melatonin, causing increased or prolonged sedation.
  • Talk to your doctor if you experience any unusual reactions after taking melatonin.
  • Melatonin should only be used short-term unless a doctor has advised you to take it long-term.
  • Do not take melatonin if you are pregnant and do not use it if you are breastfeeding unless on a doctor's advice.

6. Response and effectiveness

  • Drowsiness may be experienced within 30 minutes of taking melatonin and generally persists for at least an hour.
  • Supplements of 5mg increase peak melatonin levels by around 25 times; however, they do not alter the natural physiological release of melatonin.
  • Plasma levels of melatonin return to normal within 24 hours of a single dose of melatonin.

7. Interactions

Medicines that interact with melatonin may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with melatonin. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with melatonin include:

  • echinacea
  • fluvoxamine
  • hormones, such as estrogens or hydroxyprogesterone
  • ifosfamide
  • medications that also cause sedation, such as alprazolam, clobazam, diazepam, midazolam, temazepam, zaleplon, or zolpidem
  • PARP inhibitors, such as olaparib
  • some quinolone antibiotics, such as moxifloxacin
  • warfarin.

Note that this list is not all-inclusive and includes only common medications that may interact with melatonin. You should refer to the prescribing information for melatonin for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use melatonin only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: August 29, 2023.