Magnesium toxicity primarily presents with which effect?

• A. Hypercalcemia.
• B. Seizures.
• C. Hypertension.
• D. CNS depression.

Answer: (D)

Magnesium toxicity mainly depresses the central nervous system. When magnesium levels become too high, the body’s calming effect on neural activity leads to drowsiness, lethargy, and a decreased level of consciousness. As toxicity progresses, deep tendon reflexes fade, and there can be respiratory depression and even cardiovascular instability like hypotension and bradycardia. This CNS-dominant effect is why CNS depression is the best answer.

Hypercalcemia is not typical of magnesium toxicity; magnesium excess doesn’t usually cause seizures—it actually has anticonvulsant properties, which is why high magnesium levels prevent seizures in conditions like preeclampsia. Hypertension is also not the hallmark—toxicity tends to cause hypotension due to vasodilation. In clinical practice, when administering IV magnesium, closely monitor reflexes, respiratory status, level of consciousness, and serum magnesium to catch toxicity early.