What is the mechanism of interaction between calcium and levothyroxine?

Calcium reduces levothyroxine efficacy by forming insoluble complexes that can inhibit the absorption of levothyroxine in the gastrointestinal tract. When calcium is ingested alongside levothyroxine, it can bind to the medication, which limits its bioavailability and effectiveness. This interaction is clinically significant, as it may lead to inadequate thyroid hormone levels in patients who are being treated with levothyroxine for conditions such as hypothyroidism. As a result, it is commonly advised that patients separate the intake of calcium supplements or calcium-rich foods from the timing of their levothyroxine doses to ensure optimal absorption and effectiveness of the medication.