I want if you could tell me im taking natures promise mega magnesium 400 mg and it says to take it three times a day so ive been taking it every six hours is that safe?

If you're a healthy person, why are you taking so much magnesium? That is way too much magnesium to take as a simple daily supplement and can be dangerous if one has kidney disease. Troublesome diarrhea can be caused by that dose. Rarely we prescribe more than 400 mgs unless patients have severe magnesium deficiency from diuretics or long term vomiting or diarrhea.