Melatonin is a hormone, produced in the brain, that carries out a wide range of roles in the body; the most well known of its functions is the control of circadian (daily) rhythms.

Melatonin is also used medically in a number of conditions, including radiation exposure, Alzheimer's disease, and tinnitus.

Produced in the pineal gland in the brain, melatonin helps control sleep-wake cycles. Some foods contain melatonin, and it is also available as a pill.

In this article, we will look at melatonin's role in the human body, why people take melatonin pills, along with any side effects and warnings.

Fast facts on melatonin

Here are some key points about melatonin. More detail and supporting information is in the main article.

  • Initially, melatonin was extracted from cow pineal glands.
  • Melatonin supplements cause very few side effects, but they can interact with other drugs.
  • The primary medical use for melatonin is to treat sleep disorders.

Melatonin has a number of roles in the human body, including regulating sleep.Share on Pinterest
Melatonin has a number of roles in the human body, including regulating sleep.

Of melatonin's many functions, the best understood is the part it plays in maintaining circadian rhythms.

In humans, the circadian "clock" is found within the hypothalamus in an area called the suprachiasmatic nucleus (SCN).

Using the daily cycle of light and dark, the SCN creates and maintains a daily cycle.

Certain hormones are released at specific times of the day. In the late afternoon and early evening, hormones are released that prepare the body for sleep. During the early hours of the morning, the body starts to prepare for waking and activity.

Information regarding light levels reaches the SCN and is then passed to the pineal gland deep in the center of the brain. The pineal gland releases melatonin at night and suppresses its release during daylight.

Even when a human is kept away from all external light sources and time references, the body maintains a natural rhythm of around of 24 hours and 11 minutes.

Other roles of melatonin:

  • Melatonin is a potent antioxidant.
  • Melatonin can form complexes with metals including cadmium, aluminum, and copper. The importance of this is not yet understood.
  • Immune system - melatonin is known to have a role within the immune system, but the exact processes are not yet known. It has an anti-inflammatory action.
  • Protective role in neurodegenerative diseases and acute pancreatitis.
  • Regulates fat cells.

Receptors for melatonin are present in the brain, cardiovascular system, liver, intestine, and kidneys, so melatonin clearly works across many systems.

Because melatonin appears to have limited side effects, is naturally occurring, and relatively easy to synthesize, it has been tested on a number of medical conditions.

Below are some of the current conditions being investigated for their reaction to melatonin.

Sleep disorders

A variety of sleep problems have been treated with melatonin with varying success rates.

Insomnia in children and older adults, jet lag, and delayed sleep phase syndrome (a disorder where the circadian rhythms appear to be too long) seem to be particularly responsive to melatonin.

Children with autism can have abnormal melatonin pathways and lower than normal melatonin levels.

Some studies have shown that melatonin helps improve sleep duration, reduce the time taken to drift off to sleep, and reduce the number of night-time awakenings in these children. However, much of the research has been conducted using self-reported levels of improvement; more investigation in this area needs to be done.

Despite the importance of melatonin in natural sleep cycles, taking melatonin as a supplement without an underlying condition does not seem to improve or extend sleep.

Melatonin has very few side effects. A number of clinical trials have investigated short-term, low-dose, and up to 3-month usage and found no adverse events. However, some side effects have been reported, such as:

  • headaches
  • nausea
  • dizziness
  • drowsiness
  • irritability

Some studies on older adults noted side effects that include:

  • restless legs
  • skin pigmentation
  • thrombosis (blood clots)

Because melatonin may affect the reproductive system, it is not recommended for use among people who wish to become pregnant or breast-feeding mothers.

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Melatonin can interact with other medication.

Some individuals should avoid melatonin, these include:

  • Patients who are taking medication to lessen bleeding, prevent blood clotting, or to moderate blood pressure are advised to avoid melatonin.
  • Melatonin might interfere with blood sugar levels and is therefore not recommended for people with diabetes.
  • Melatonin might increase the risk of seizures in people who have a seizure disorder.
  • Because melatonin influences the immune system, it is not recommended for people who are taking immunosuppressant drugs, for instance, transplant patients.
  • Melatonin may worsen bleeding disorders, such as hemophilia.
  • Melatonin may worsen symptoms of depression in some individuals.
  • People who are using ACE inhibitors are also recommended to avoid melatonin.
  • Melatonin might increase any drowsiness that occurs as a side effect of other drugs, such as benzodiazepines, codeine, alcohol, and barbiturates.

Other than sleep disorders, scientists are looking at other conditions where melatonin might be able to help; these conditions include:


There is a small amount of evidence that melatonin can relieve some headaches, in particular, cluster headaches (severe and recurrent pain on one side of the head, often surrounding the eye).


Some clinical studies of colon, breast, renal, brain, and lung cancer imply that melatonin might work as an anticancer agent in conjunction with chemotherapy and radiation therapy.

A literature review and meta-analysis carried out in 2005 found that the "substantial reduction in risk of death, low adverse events reported, and low costs related to this intervention suggest great potential for melatonin in treating cancer."

Alzheimer's disease

Melatonin levels decrease with age across the population, but this reduction is more pronounced in patients with Alzheimer's disease. Research has shown that melatonin appears to slow the cognitive decline associated with Alzheimer's.


There is some evidence that the effects of tinnitus could be slightly improved by melatonin, perhaps due to improved sleep or its antioxidant properties.

Gallbladder stones

Melatonin carries out a number of roles in the gallbladder, including the conversion of cholesterol into bile and helping gallstones move through the gallbladder.

Free radical damage is known to increase the chances of gallstone development. Melatonin's antioxidant properties may be beneficial.

Protection from radioactivity

Much of the damage inflicted by contact with radioactive substances is caused by free radicals. In this respect, melatonin might be useful for patients undergoing radiation therapy or for those who work in high-radiation areas.


Melatonin clearly has many functions within the human body, most of which we are yet to understand. It also seems that melatonin might be useful in the treatment of some illnesses. No doubt, in time, its full potential within the pharmaceutical world will become clear.