We present a case of magnesium toxic effects that demonstrates the wide spectrum of associated clinical signs and symptoms. As shown by the case report, the literature review, and the MEDWATCH database, physicians frequently neglect to consider hypermagnesemia in the differential diagnosis of this clinical presentation. Abnormal renal function is a well-known risk factor for the development of hypermagnesemia. This case report highlights several associated nonrenal risk factors for hypermagnesemia, which include age, gastrointestinal tract disease, and administration of concomitant medications, particularly those with anticholinergic and narcotic effects. This case report also demonstrates how consumers may misuse magnesium-containing over-the-counter drug products. In addition, physicians may not inquire about and patients may not volunteer over-the-counter medications in a complete drug history. However, the morbidity associated with hypermagnesemia as well as its reversibility make it an important diagnostic consideration for elderly patients with gastrointestinal tract disease, regardless of renal function. For easy reference for both consumers and health-care personnel, we provide a list of over-the-counter drug products that contain significant amounts of magnesium.