Melatonin supplements are frequently used as a sleep aid for insomnia, work shift sleep disorder, and jet lag. The supplements are available at most pharmacies and drugstores and are typically regarded safe for short-term use; however, patients should take note of possible negative side effects. If you are taking any other supplements, medications or have a medical condition, you should consult your physician before using melatonin.
According to the Mayo Clinic, melatonin supplements may cause daytime drowsiness. This side effect can be corrected by taking a lower dose, but you should use extreme caution when driving or operating heavy machinery.
Changes in Sleep
Some patients experience nightmares, vivid dreams and sleepwalking while taking melatonin supplements. Sleep-related symptoms typically cease once you stop taking melatonin. Overuse or incorrect use of melatonin supplements may disrupt the circadian rhythm, thus causing irregular sleep-wake cycles. Melatonin levels are higher in the blood prior to bedtime; a dark room or suppressed lighting causes melatonin chemicals from your brain to release. Since the brain releases melatonin chemicals automatically once you enter darkness, it can be very easy to incorrectly use melatonin supplements.
Melatonin is known to cause changes in the level of hormones such as luteinizing hormones, progesterone levels and other hormones controlled by the pituitary gland. Women who are pregnant, nursing or attempting to become pregnant should avoid melatonin supplements. Excessive melatonin use during pregnancy may lead to developmental disorders in the baby, and high levels of melatonin may have a contraceptive effect on those hoping to conceive. Men using the supplement may notice a decrease in sperm count, decreased sperm mobility and increased breast size. Both men and women may experience a decrease in sex drive.
According to MedlinePlus, melatonin can cause mood changes such as sadness or giddiness, and worsen existing symptoms of depression. These side effects are commonly associated with overdosing on melatonin supplements. Delusion, paranoia and hallucinations have been reported in some cases. If you have a history of psychotic disorders or depression, you should consult your physician prior to taking melatonin supplements.
Cholesterol and Blood Pressure
Melatonin supplements may increase cholesterol and decrease blood pressure. Patients with type 1 diabetes have reported elevated blood sugar levels while taking melatonin. Even low doses of melatonin may reduce glucose tolerance and insulin sensitivity. Arrhythmia is often associated with regular use of melatonin supplements.
Melatonin may negatively interact with various common medications including antipsychotic and antidepressant medications, steroidal medications, birth control pills, anti-inflammatory medications, blood thinning and blood pressure medications. Patients on any of these drugs should consult their doctor before taking the supplement. Melatonin may also interact with tobacco, caffeine, alcohol and other commonly used substances.
Disorientation and Seizures
According to MedlinePlus, taking melatonin supplements can cause disorientation and increase the risk of having seizures. These side effects are often reported with overdosing on melatonin supplements, so these are not common side effects, but could be very likely to happen if used incorrectly. Consumers who have a known seizure disorder should only use melatonin supplements under close supervision of a physician.
Increased Risk of Autoimmune Disorders
Melatonin supplements have also been linked to an increased risk of autoimmune disorders such as autoimmune hepatitis, and even to triggering Crohn's disease symptoms. According to MedlinePlus, users have reported stomach cramping, nausea and vomiting.