I prefer 250mg every other day (and lower if I could find it, as I already take a daily multivitamin). I take it mainly to help regularity since I take a low dose iron tablet also every other day which can have constipating effects. On two separate occasions now (one recently), I grabbed 400 mg off the store shelf out of convenience or cost. Both times after about 10 days, I realize I have felt weaker than usual, more jelly-legged, accompanied by some diarrhea. I then thought of the increase in my Magnesium, and read where those are signs of too much Magnesium. So I have purchased the lower dose, and things are back to "my" normal. I hope now to remember to be careful about not rocking the boat by making changes like that. I'm not suggesting this has the same effect on everybody, as we all have so many variables affecting us, but I think it has an effect on me.