E.B.
We have extensive experience with sleep disorders/sleep problems. We have gotten a tremendous amount of info from the hospital on Melatonin, and I'm happy to pass along what we've learned.
First off, Melatonin is not regulated by the FDA or any other agency. It's not a drug, it's a hormone that we all make, and the Melatonin you can buy on the shelf is supposed to be identical to that hormone. So if the Melatonin you're buying says FDA approved, that should be a warning that you're not buying a reliable supplement, because the FDA does not approve any Melatonin substance.
Second, we were told about studies conducted on Melatonin, that could be purchased at any drugstore or health food store. Some agency (an official one but I can't remember the name) investigated the Melatonin in all the brands, and some didn't contain any, some contained too much, nearly all contained an amount of Melatonin that was different from what the bottle said, and it differed from batch to batch.
We were told to only purchase it from a company called Life Extension Foundation (www.lef.org) as they submit to outside testing and their Melatonin is trusted by the hospital. We were told if we don't buy it from there not to buy it at all (and the hospital doesn't own that company or anything else like that). It's not very expensive, just about the same as the stuff you can buy at Costco or Rite Aid or Walgreen's.
Next, the Melatonin is supposed to be given about 4 hours or 5 hours before bed. There are two forms of it, instant release and timed release. The instant release is supposed to be given the 4 or 5 hours before the desired bedtime. It's not like a sleeping pill. It's not like Benadryl.
We use 3 mcg (micrograms) 5 hours before bedtime. The people at Life Extension Foundation were really helpful.
We haven't seen appetite changes, but if you're buying Melatonin that doesn't contain the proper amount, or could contain other ingredients, that could explain that.
I hope this helps a little! We've done two sleep studies so far and we have to use another medication in addition to Melatonin, but we're trying to get a night's sleep! Our child's issue is more substantial.