There have been times I have taken melatonin. Here are some remarks from my website (<a target=_blank class=ftalternatingbarlinklarge href="http://www.healthgazelle.org/sleepissues.shtml">Sleep Issues</a>):
I routinely recommend that people give Co-Q-10 in the morning rather than melatonin at night or, in extreme casese, give Co-Q-10 in the morning and melatonin at night. Co-Q-10 is the co-enzyme for melatonin and wakes the brain up in the morning. People are very prone to being deficient in it because it is made in the body in a complex 17 step process, so lacking something at any stage can cause a deficiency. If you take Co-Q-10 in the morning, about 12 hours later the body will produce more melatonin -- so, ideally, it should be given about 12 hours or so before the desired bedtime. However, if you give melatonin in the evening, it does NOT cause the body to produce more Co-Q-10.
My personal experience and the experience of my oldest son is that melatonin by itself made us too sleepy and we could not fully wake up for 2 or 3 days after taking it. I regularly take Co-Q-10 but only successfully took melatonin for about a month or two when bad withdrawal symptoms from stopping medication were making it impossible for me to sleep AT ALL for 3 or 4 weeks. During that time, my brain chemistry was so fried that I desperately needed help to make it go to sleep. Some autistics have similar issues. But if the sleep issues are not real extreme, I think giving Co-Q-10 as a first step can more gently help establish a healthy daily cycle of brain chemicals for the waking and sleeping cycles.