<p>Absorption of orally administered T4 from the gastrointestinal tract ranges from 40% to 80% with the majority of the levothyroxine dose absorbed from the jejunum and upper ileum. T4 absorption is increased by fasting, and decreased in malabsorption syndromes and by certain foods such as soybeans, milk, and dietary fiber. Absorption may also decrease with age. In addition, many drugs affect T4 absorption including bile acide sequestrants, sucralfate, proton pump inhibitors, and minerals such as calcium (including in yogurt and milk products)<sup class="text-reference-group"><a class="reference-popover-link" data-content="Chon DA, Reisman T, Weinreb JE, Hershman JM, Leung AM: Concurrent Milk Ingestion Decreases Absorption of Levothyroxine. Thyroid. 2018 Apr;28(4):454-457. doi: 10.1089/thy.2017.0428. Epub 2018 Mar 28. (PubMed ID 29589994)" href="#reference-A179617">3</a></sup>, magnesium, iron, and aluminum supplements. To prevent the formation of insoluble chelates, levothyroxine should generally be taken on an empty stomach at least 2 hours before a meal and separated by at least 4 hours from any interacting agents. </p>