Nervous system side effects have resulted from the suppression of neuromuscular transmission in the CNS and at the neuromuscular junction by magnesium (antagonized by calcium). The degree of severity of these side effects has been dependent on the serum magnesium level. Clinically, if serum magnesium (Mg) levels increase to 4 to 7 mEq/L, there may be a decrease in tendon reflexes, muscle weakness and/or mental confusion/sedation.