Magnesium is a central mineral and also interacts with sodium and potassium. There have been reports from people who use magnesium then start having problems. Usually this is with adrenal people, the idea is that sodium and potassium stores can be changed with magnesium.
Magnesium is also antagonistic to calcium meaning it can reduce calcium stores. The inverse is true as well (calcium supplementation reduces magnesium).
It is important to include all nutrients which includes adequate mineralization, vitamin co-factors, fats (healthy) and protein. These are raw materials that the body needs. There is an inter dependency among nutrients which means if something is missing then the whole organism is affected.
Vitamin D is synergistic to magnesium. The forms of magnesium can be different and there are some forms that seem to be better such as lysinate, glycinate for example.