Abstract
Introduction: Levothyroxine has a narrow therapeutic window, and its absorption is highly sensitive to food and supplements, making precise dosing and adherence to administration guidelines critical. The CONTROL Surveillance II study evaluated real-world patient awareness and adherence to FDA-labeled levothyroxine administration instructions, including timing and avoidance of interfering substances. This sub-analysis assessed patient ingestion of foods, vitamins, and supplements known to affect absorption, the effectiveness of physician communication, and patient comprehension and recall, as well as demographic and socioeconomic characteristics associated with lower awareness.
Methods: CONTROL Surveillance II was an online survey of 1,000 U.S. adults aged 19–90 years who self-reported a clinician diagnosis of hypothyroidism. Participants were randomly selected from a proprietary, consented research panel developed and maintained by Harmon Research Inc., a U.S.-based research firm (https://www.harmonresearch.com). Pregnant patients were excluded. Qualified subjects had been taking levothyroxine monotherapy for ≥ 1 year. Survey questions were reviewed by board certified endocrinology experts, and the survey was initiated in December 2023 and completed in January 2024.
Results: This CONTROL Surveillance II sub-analysis assessed patient awareness of food, vitamin, and supplement interactions with levothyroxine, provider communication, and factors associated with nonadherence. Key findings include: 1. Overall, 49% of participants reported using dietary supplements, most commonly multivitamins (57%), followed by calcium (30%) and iron (15%). 2. Most patients recalled receiving physician guidance on dosing timing, but only 45% remembered discussions about food, vitamin, or supplement interactions with levothyroxine. 3. Supplement use was higher among older adults (29% vs 14%, P≤ 0.05), non-Hispanic white patients (27% v 18%, P≤ 0.05), and higher income participants, with the latter reporting greater multivitamin and calcium use than lower-income groups (63% vs 54% and 39% vs 28%, P≤ 0.05).
Conclusions: Suboptimal levothyroxine administration due to supplement and food co-administration is widespread. This sub-analysis highlights persistent gaps in counseling and comprehension influenced by sociodemographic factors, underscoring the need for improved patient education.