I've heard that if you take this for years, which I did, though at a small dose (around 12 mg) that your natural sleep hormones will shut off. I trusted my doctor who said that I can take it long-term. So, I did, for about 5 years. Then, I started noticing more missed menstrual cycles (I always had PCOS, but just didn't know it.). I've read that melatonin can cause reproductive dysfunction, and so I'm worried about having taken it for so long. I know I shouldn't have blindly trusted my doctor w/o reading into myself. I don't know if my PCOS worsening has anything to do with melatonin, but I do know that in the year or so I've been off it altogether, my sleep is worse than it's ever been. I can sleep, but it's very difficult getting to sleep. What is the deal - is it true that it can have these hormonal effects, even at a small dose?