I've used melatonin for a couple years now. It worked well for the first year, but over the last several months it can take 4 or 5 hours before it takes effect. I have no idea why, and it is the same with all my meds. It seems to stay in my system for 12 - 14 hours. With the delayed reaction, that can mean I still feel the effects until a few hours before bedtime the next day. I'd be curious if anyone else has this happen with them too. Take Care, David Meigs [log in to unmask]