Melatonin is an unregulated supplement commonly used by people who have trouble sleeping. While studies suggest melatonin does not cure insomnia, it may be effective for sleep disorders such as jet lag and delayed sleep phase syndrome. When used inappropriately, melatonin can cause temporary negative side effects to your sleep health. As there are also many counterindications with other pharmaceuticals, consult your physician if you are considering melatonin supplements.

Next-Day Drowsiness

Most people report feeling more alert after taking melatonin. However, for others, melatonin may cause persistent sleepiness the day after use. If you are sleepy the day afterward taking this supplement, your dosage may be too high and you should talk with your doctor about adjusting it. Do not operate heavy equipment for up to five hours after taking melatonin, advises the National Institutes of Health.

Bad Dreams

Because melatonin affects sleep cycles and moods, dreams may be more intense than normal. Bad dreams and nightmares have been reported by melatonin users, according to Dr. Brent A. Bauer, a Mayo Clinic internist. If you are sensitive to bad dreams, melatonin is not for you.

Sleepwalking

Some people report higher instances of sleepwalking while using melatonin supplements. Sleepwalking, or somnambulism, is common in children but usually disappears after puberty. Sleepwalking occurs during deep sleep and is not remembered afterward. However, people can hurt themselves during sleepwalking episodes. Some sleepwalkers have been known to drive their vehicles.

Aggravation of Sleep Disorders

Ironically, melatonin can worsen sleep disorders in some people, especially if taken for long periods and at high doses, according to research published in the "Journal of Biological Rhythms." Thus, melatonin cannot be considered a cure-all sleep supplement. If you suffer from consistent problems with getting enough sleep, consult your physician before using melatonin.