What are the issues with melatonin?

Melatonin is a naturally occurring hormone that induces sleep. Your body converts dietary tryptophan into serotonin during the day, and melatonin at night. Instead of taking supplements, allow your body to follow natural circadian rhythms of light and dark periods.

I think that melatonin is generally considered pretty safe, but like any substance people can be allergic to it. Also if you are diabetic or have high blood pressure or are taking certain antidepressants you might want to take certain precautions. Look up melatonin side effects in a Google search. the WEDMD site (and others) can provide details.