What are the side effects of taking Melatonin?

Has anyone of you tried this yet? What are the side effects you experienced?

I have taken it before sleep apnea but I stopped using it years ago. I started with 2.5 mg, I would split a 5 mg in half. It wasn’t long and I went to 5. I didn’t have any problems or side effects from it, that I noticed. I always said the best night of sleep I ever had was Melatonin and Benadryl. I didn’t even think about it when I took it. My allergies were flaring up and I took a Benadryl before I took a Melatonin. One Benadryl can knock me out then in and out for the following 24 hours. I survived but had a “hangover” for about a day and a half. I went back to the Melatonin and I took it for years. My doctor finally gave me Ambien because he said Melatonin isn’t a “clean” drug. They aren’t FDA approved so you don’t really know what is in it or how much you are actually taking. But I didn’t have any side effects.

I’ve read that this is safe to intake and it doesn’t really have side effects but the effectivity itself to sleep depends on person to person. Some claim they benefit from it, and some say they didn’t find it helpful at all and that’s especially those who are suffering from sleep disorders already.

My OH took it, too. It worked for him for awhile then he just didn’t seem to get any help from it. He hasn’t been diagnosed with any sleep disorder.

Well, I have read it is a hormone.
Tried at a tiny dose (1mg?), but after the second night, had strange, sad dreams. Stopped it. Slept and dreamt normally after stopping it.
APAP alone, no ramp, works best for me. Aim for 8 hrs, average 7+. Simple.
I appreciated the interesting comments here about its contents not being standardized.