I am wondering how much magnesium I could take to keep my blood pressure in check. I have been taking 400 mg before breakfast. Is is feasible that I take another 400 mg at bedtime? Also with the magnesium I'm taking 600 mg calcium. My blood pressure has been at normal levels except for an occasional spike out of nowhere. Any suggestions? I can't tolerate medication - atenolol was the worst. Therefore my thoughts are that if perhaps I take 800 mgs of mag a day, that may eliminate occasional spiking. Right or wrong?