Long-term use of PPIs — defined as more than one year of regular use — significantly impairs the body's ability to absorb magnesium through the intestinal wall. This occurs because PPIs reduce stomach acid, and adequate stomach acid is required for proper magnesium absorption. The FDA issued a safety warning about this interaction in 2011, after multiple reports of severe hypomagnesemia (dangerously low magnesium levels) in long-term PPI users — even patients who were taking magnesium supplements alongside their PPI. In the most serious cases, low magnesium caused by PPIs has produced life-threatening arrhythmias, seizures, and muscle spasms. Anyone taking a PPI regularly for more than a year should have their magnesium levels monitored periodically by their doctor, and anyone on a PPI who also takes a magnesium supplement should ensure their physician is aware of both.
5. Levothyroxine — Thyroid Medication
Levothyroxine — sold under brand names including Synthroid, Levoxyl, and Euthyrox — is the standard medication for treating hypothyroidism, a condition in which the thyroid gland does not produce sufficient thyroid hormone. It is one of the most prescribed medications in the United States, and it requires careful dosing and consistent absorption to maintain stable thyroid hormone levels in the blood. Even small variations in levothyroxine absorption can shift a patient from properly treated to under- or over-treated, with significant health consequences.
Magnesium-containing antacids can reduce stomach acid sufficiently to impair levothyroxine absorption, since adequate gastric acidity is required for the medication to dissolve and be taken up by the intestine properly. Additionally, some forms of magnesium may directly bind to levothyroxine in the digestive tract. The standard recommendation is that levothyroxine should be taken on an empty stomach first thing in the morning — at least 30 to 60 minutes before eating or taking any other supplements or medications — and that magnesium supplements should be taken at least 4 hours after the levothyroxine dose. Patients who take both and do not observe this separation may find that their thyroid levels are consistently below target despite apparently adequate medication doses.
