Can i take 1000mg of magnesium a day? it's 250% of my rda. i want to take it daily for bad period cramping. is it ok?

Yes, however...: There is no danger in taking too much magnesium (unless you have kidney failure). The only side effect you are likely to encounter is diarrhea/loose stools if you take more than you can absorb. If you take a well-absorbed form you may not need to take that much. I advise Magnesium glycinate or taurate for optimal absorption. See http://drcarolyndean.com/magnesium_miracle/ for more info.