I've had some pretty bad PEM recently and I started taking Magnesium [lactate] just before that happened. I read elsewhere that Magnesium actually is supposed to HELP with muscle cramps, but can it also have a negative affect? In the past I took D-Ribose mixed with Magnesium and that didn't go too well for me either. I'm starting to wonder if Magnesium does not work with me well. I stopped taking Magnesium lactate this morning.