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Role of melatonin

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NIH NCCIH melatonin what you need to know safety 2025

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Melatonin is a hormone made mainly by the pineal gland. Its primary role is to signal biological night and coordinate the body’s circadian rhythm, especially the sleep-wake cycle.

Main roles

  • Regulates timing of sleep: secretion rises in darkness and is suppressed by light. It helps align sleep with the night-time portion of the circadian cycle. The suprachiasmatic nucleus (SCN), the brain’s circadian clock, regulates this release. Harrison’s Principles of Internal Medicine, 22E, p. 45.
  • Promotes sleep onset: it tends to make a person sleepy and can improve sleep efficiency when the internal clock is delayed or misaligned.
  • Resets the body clock: useful for circadian rhythm problems such as:
    • Jet lag
    • Shift-work related sleep disturbance
    • Delayed sleep-wake phase disorder
    • Non-24-hour sleep-wake disorder, particularly in some blind individuals
  • Seasonal signaling: the duration of melatonin secretion reflects night length and contributes to seasonal biological rhythms.
  • Other physiological effects: melatonin receptors and production occur outside the pineal gland, including in the retina and gastrointestinal tract. It may have antioxidant actions, but claims for anti-aging, cancer treatment, or broad disease prevention are not established indications. Kaplan and Sadock’s Synopsis of Psychiatry, p. 2067.

Important clinical point

Melatonin is mainly a timing signal, not a strong conventional sleeping pill. It may help someone fall asleep when their body clock is out of sync, but often has limited benefit for primary chronic insomnia if circadian timing is normal. Harrison’s Principles of Internal Medicine, 22E, p. 45.

Adverse effects and cautions

Possible effects include daytime drowsiness, fatigue, dizziness, headache, vivid dreams, irritability, and occasionally confusion or sleepwalking. Short-term use appears reasonably safe for many adults, but long-term safety is less certain. Seek medical advice before use in pregnancy or breastfeeding, epilepsy, or when taking anticoagulants or other medicines, as noted by the NIH NCCIH safety guidance. Keep gummies and other supplements away from children.
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