Melatonin Risks & Side Effects

Melatonin, a naturally occurring hormone that regulates the body’s internal clock, is also used to treat sleep disorders and a number of other health issues. Synthetic melatonin supplements can help adjust sleep cycles in autistic, mentally retarded and blind people, as well as those with jet lag and may improve insomnia. Melatonin does have a number of side effects and risks, some potentially serious. Starting with a very low dose, no more than your body produces daily, or 0.3 mg, may help reduce symptoms, the University of Maryland Medical Center website advises.

Sleep Disturbances

Melatonin can cause nightmares, sleepwalking or very vivid dreams. Daytime sleepiness can also occur but may improve if you decrease the dose, the University of Maryland Medical Center website states. Taking too much melatonin can also disrupt your body's circadian rhythms, or internal clock. Disorientation and confusion can also occur.

Mood Changes

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Melatonin can cause mood changes, including irritability, worsening depression, sadness of giddiness. Psychotic signs such as hallucinations and paranoia can also occur, possibility as a result of an overdose of the drug, MayoClinic.com reports.

Hormonal Effects

Melatonin might interfere with both male and female fertility by interfering with normal hormone levels such as estradiol, progesterone, luteinizing hormone, prolactin, cortisol and thyroid hormone. Because of its effects on other hormones, children, particularly adolescents, should not take melatonin, which could interfere with development in adolescence. Pregnant women should also not take melatonin, due to its effects on hormone levels. The drug can disrupt ovulation in women and may also decrease sperm count and motility in males. Melatonin can also decrease sex drive and may cause gynecomastia, increase in breast size in men.

Stomach Distress

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Melatonin can cause stomach problems, including nausea, vomiting or stomach cramps. Melatonin may also trigger Crohn’s disease symptoms, MayoClinic.com warns. Crohn’s disease, an inflammatory bowel disease, can cause abdominal pain, diarrhea, rectal pain and fever.

Medication Interactions

Melatonin can interfere with a number of medications. Taking sedative medications with melatonin may cause excessive sleepiness or sedation. Melatonin can also reduce the effectiveness of blood pressure medications and may raise blood pressure in people taking certain medications, MedlinePlus states. Melatonin can act as an anticoagulant or blood thinner. Taking melatonin with blood thinners such as heparin or warfarin can cause excessive bleeding or bruising. Melatonin can also decrease the effectiveness of steroids and immunosuppressant medications.