Thank you all for posting your stories. Almost three months after starting to take melatonin almost nightly as a sleep aid, I began a bout of horrible diarrhea that only ended last week after stopping the melatonin two weeks earlier. I never connected the melatonin with my problem so I never mentioned it to my doctor who did stool samples, blood tests, etc., which were all negative. Finally, in searching my mind, I told her about the melatonin and she told me to stop taking it. That's when I found this forum. Since then I learned that it is not be be used as a regular sleep aid, especially long term.
Again, thank you all for posting. Your stories helped confirm my problem.