Melatonin-Side Effects

Written by Tanya Thomas, B.Com | Medically Reviewed by dr. reeja tharu, M.Phil.,Ph.d on Apr 19, 2013
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Melatonin - Side-Effects

Speculation is rife about the possible side-effects of melatonin. Just like the benefits listed previously, contradictory research results have also surfaced regarding the negative consequences of supplemental melatonin. Whether a patient actually requires synthetic melatonin or not should be discussed with a qualified and trusted caregiver, in light of the following adverse associations. It should be noted here that it is difficult to estimate the long-term effects of a hormone; therefore self-prescription is strongly advised against.

The most common side-effects of taking melatonin result due to incorrect usage of the hormone. Daytime drowsiness, dizziness, stomach cramps, headaches and irritability have been reported. More serious side-effects include-

  • Gynecomastia (ie breast enlargement in men),
  • Decreased libido,
  • Lower sperm count and sperm mobility
  • Nightmares
  • Daytime drowsiness
  • Headache
  • Depression

Studies also recorded that discontinuation of the supplements reversed gynecomastia.

It is expected by several researchers that long-term use of hormonal supplements may adversely affect both male and female fertility. (Contrasting studies tout melatonin as a cure for infertility; others suggest that it can be used as an effective, side-effect-free oral contraceptive for women!) Pregnant and nursing women are also advised against the use of melatonin, since its effects on the foetus and the newborn remain unknown.

While certain studies have indicated that the pineal hormone can be used in treatment of epilepsy, others have pointed out to a striking increase in the number of seizures due to melatonin supplements, especially in children with neurologic disorders.

Results of recent research studies have contested the notion that melatonin supplements alleviate symptoms of depression; according to them, the hormone in turn aggravates it. Also, melatonin and anti-depressants form a potent cocktail for potential health complications.

Also, modern research has questioned the very premise that the body’s melatonin production declines with age. Hence, the elderly should opt for supplements only on the advice of a qualified medical practitioner. Also, blood levels of the hormone should be monitored on a regular basis.

Melatonin studies have also tentatively put forward that its long-term use may cause irreversible damage to the retina of the eye.

Melatonin supplements should not be taken by:

  • Pregnant or breast-feeding women
  • Individuals with an autoimmune disease, like lupus
  • Persons with depression
  • Patients with schizophrenia
  • Diabetics, as it increases chances of reduced glucose-tolerance.
  • Individuals prone to migraines
  • Persons with an eye disease, like retinitis pigmentosa
  • Persons whowork with heavy machinery, as long-distance drivers, pilots etc

Research has thrown up both positive and negative drug interactions for melatonin supplements. These include interactions with-

  1. anti-depressants,
  2. certain chemotherapy drugs,
  3. anticoagulants, steroids,
  4. anti-psychotic drugs, and
  5. with blood pressure and immunosuppressant medications.


  1. University of Maryland Medical Center - (
  2. Family doctor - (
  3. The Annie Appleseed Project - (
  4. Talk about Sleep - (
  5. Priory Medical Journals - (
  6. Society for Light Treatment and Biological Rhythms - (

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