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Biology LibreTexts

15.6.1.9: Melatonin and the Pineal Gland

The pineal gland is a tiny structure located at the base of the brain. Its principal hormone is melatonin, a derivative of the amino acid tryptophan.

Synthesis and release of melatonin is

  • stimulated by darkness
  • inhibited by light.

But even without visual cues, the level of melatonin in the blood rises and falls on a daily (circadian) cycle with peak levels occurring in the wee hours of the morning. However, this cycle tends to drift in people who are totally blind — often making them sleepy during the day and wide awake at night. Giving melatonin at bedtime has proved helpful in a number of cases

Melatonin is readily available in drug stores and health food stores, and it has become quite popular. Ingesting even modest doses of melatonin raises the melatonin level in the blood to as much as 100 times greater than normal. These levels appear:

  • to promote going to sleep and thus help insomnia
  • to hasten recovery from jet lag
  • not to have dangerous side effects

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