I was surprised to find that the peer-reviewed FEBS Journal (of the Federation of European Biological Societies) is available to all. The article I have linked here-- http://www3.interscience.wiley.com/cgi-bin/fulltext/118634749/PDFSTART --is a long review of melatonin studies, which turns out to be more useful and versatile than I knew.
Some of you might be interested in its use in anti-depression, anti-SAD, anti-breast cancer, and so on (the rest of us). I have a system in which I use it in anti-jet lag (the article discusses this, too) and in its chronobiotic effects every night.
Re St. John's wort: I advise O-blood types against using it as it is an "avoid" for them. I tried it years ago and began to feel quite psychotic (actually, I'm not at all sure what that word really means since that has never been my experience). In any case, I felt quite loopy (about THAT I know a bit more!). Seriously, I very much disliked the garbled, befogged, tangled mental experience of using St. John's wort and trust the advice of the blood-type regimen. Other blood types can use it.