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By: AAST Associate Editor on March 11th, 2021

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Melatonin ― The Hormone of Darkness

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Known as the "hormone of darkness," melatonin, a natural-occurring hormone primarily released by the brain's pineal gland at night, is commonly taken as an oral supplement for the treatment of insomnia and other sleep disorders. It is by far the most used sleep aid used in the United States, with 3 million Americans using it in 2012, according to a nationwide survey from the U.S. Centers for Disease Control and Prevention. Questions remain, however, as to its effectiveness; it has been found that while it may induce sleep faster in some people, it may not necessarily improve overall sleep maintenance or increase sleep duration.

One review of 15 studies involving 284 otherwise healthy subjects found that those who took melatonin before bed fell asleep 3.9 minutes faster on average and slept 13.7 minutes longer. Another analysis of 19 studies involving nearly 1,700 adults and children diagnosed with primary sleep disorders, found that melatonin users fell asleep seven minutes faster on average and slept eight minutes longer. A third study looked at 116 men with delayed sleep-wake phase disorder and found that those who took 0.5 milligrams of fast-release melatonin one hour before their desired bedtime at least five nights per week fell asleep 34 minutes earlier on average, slept more soundly and saw their sleep patterns normalize after four weeks.

Who Should Consider Melatonin

Generally, those finding it difficult to fall asleep at night will benefit the most from melatonin. Research shows that a supplement may help people with insomnia fall asleep slightly faster and may have bigger benefits for those with delayed sleep phase syndrome, according to Johns Hopkins Medicine. “Your body produces melatonin naturally. It doesn’t make you sleep, but as melatonin levels rise in the evening it puts you into a state of quiet wakefulness that helps promote sleep,” explains Johns Hopkins sleep expert Luis F. Buenaver, PhD, CBSM.

A review published in the Sleep Medicine Reviews in 2017 combined the evidence from 12 randomized and controlled trials that looked at how well melatonin works to treat primary sleep disorders in adults, including insomnia, delayed sleep phase syndrome, non-24 sleep wake syndrome in people who are blind and REM behavior disorder. The researchers found sufficient evidence that melatonin can help people fall asleep faster and helped blind people regulate their sleep patterns.

A review published in 2014 in the Journal of Pediatric Psychology combined the evidence from 16 randomized controlled trials to find out if melatonin could aid children with sleep problems. Researchers found that melatonin helped children suffering from insomnia to fall asleep more quickly, wake up fewer times each night, fall back to sleep faster when they did wake up and get more sleep each night.

Is It Safe to Take Every Night?

One major advantage melatonin has over other sleep aids is that it is non-addictive. According to the National Center for Complementary and Integrative Health (NCCIH), short-term use of melatonin supplements appears to be safe for most adults and children. But information on the effects of long-term melatonin supplements is limited.

A 2016 study published in Clinical Drug Investigation indicated that long-term melatonin use in adults may cause mild side effects when compared to a placebo. Studies into the effects of long-term melatonin use in children remains limited. Because melatonin levels naturally decrease at the beginning of puberty, there are some concerns that long-term melatonin use in children may delay puberty onset. However, a study published in Nature and Science of Sleep in 2019 that looked into the issue, found no clinical studies that experimentally tested the effects of melatonin on pubertal timing in children, and only a small number of observational studies.

Downsides of Melatonin as Compared to Prescribed and FDA-Controlled Substances

Melatonin is sold as a dietary supplement, and its manufacture is not regulated by the U.S. Food and Drug Administration. A study in the Journal of Clinical Sleep Medicine examined the content of 31 melatonin supplements from different brands. Researchers found that the actual content of the melatonin supplements ranged widely compared to their labels. The researchers did not find any patterns of variations associated with specific brands. Additionally, eight of the supplements in the study contained serotonin, which is used to treat depression and some neurological disorders. Unknowingly taking serotonin can lead to serious side effects.

Dosing is also a problem. A 2005 systematic review published in the Sleep Medicine Reviews journal found that melatonin is most effective at a dose of 0.3 milligrams. But commercially-available melatonin pills contain up to 10 times the effective amount. At that dose, melatonin receptors in the brain become unresponsive.

Possible Side Effects

The Mayo Clinic lists these common side effects:

  • Headache
  • Dizziness
  • Nausea
  • Drowsiness

Other, less-common side effects include: short-lasting feelings of depression, mild tremor, mild anxiety, abdominal cramps, irritability, reduced alertness, confusion or disorientation and hypotension (abnormally low blood pressure).

Other things to note:

In addition, melatonin supplements can interact with various medications, so seek medical advice before taking if you also take:

  • Blood-thinning medications
  • Epilepsy medications (anticonvulsants)
  • Immunosuppressants
  • Diabetes medications
  • Blood pressure medications
  • Birth control medications

Melatonin's impact on pregnancy should also be considered. Both the ovaries and placenta make high levels of melatonin and use the hormone throughout pregnancy and delivery. Melatonin levels rise significantly at 24 weeks of pregnancy and rise even more after 32 weeks. Furthermore, melatonin works with oxytocin to promote labor and delivery. Melatonin levels are higher at night, which might be why many women go into labor in the evening and early morning. Melatonin is also found in amniotic fluid, and babies rely on their mother’s melatonin supply while they are in utero and until nine to 12 weeks after they are born.

Is Melatonin Right for Your Patient?

While there is evidence that melatonin can help people with certain sleep disorders fall asleep faster, it may not be sufficient to help those who have difficulty getting a proper night's sleep, or those who wake up often in the middle of the night and have difficulty falling back to sleep. If you believe that your patient could benefit from melatonin, consider first advising the patient to reduce his or her intake of electronic media consumption before bedtime. The blue light emitted by screens on cell phones, computers, tablets and televisions has been shown to inhibit the production of melatonin.

Also educate the patient regarding environmental influences on melatonin production. For example, the body may produce melatonin earlier or later in the day, depending on the season and length of the day, which can throw off the natural sleep cycle. Foods such as tomatoes, walnuts, olives, rice, barley, strawberries, cherries and cow’s milk contain melatonin. Thus, consumption of these foods may impact dosing requirements, which typically range from 1 mg to 10 mg. For insomnia, it’s best to take a melatonin supplement 30 to 60 minutes before bedtime. And remember that melatonin supplements can negatively interact with many different medications, so be sure to review the patient's current medications before recommending it.