Mg2＋在組織細胞液內為含量次多之陽離子，為體內酵素反應之重要促進因子，如缺乏則會引起身體構造上及功能上之障害。1954年Castillo ＆ Engbaek也發現Mg2＋為中樞神經抑制劑及促成Tendon reflex及End Plate之興奮度之減低因素。

Cardiac glycosides (eg, digoxin)
Administer magnesium sulfate with extreme caution because serious changes in cardiac conduction, which can result in heart block, may occur if administration of calcium is required to treat magnesium toxicity.

CNS depressants (eg, barbiturates, narcotics)
Possible additive CNS depressant effects.

Neuromuscular blocking agents
Potentiation of neuromuscular blockade.

Nitrofurantoin
Decreased absorption of nitrofurantoin (oral magnesium).

Penicillamine
Reduced penicillamine effects (oral magnesium).

Tetracyclines
Decreased absorption of tetracyclines (oral magnesium).

Incompatibility
Alcohol (in high concentrations), alkali carbonates and bicarbonates, alkali hydroxides, arsenates, barium, calcium, clindamycin phosphate, heavy metals, hydrocortisone sodium succinate, phosphates, polymyxin B sulfate, procaine hydrochloride, salicylates, streptomycin, strontium, tartrates, tetracycline, tobramycin.