OBJECTIVE: Medications may sometimes interfere with the intestinal absorption of 
levothyroxine, primarily by forming an insoluble complex with the thyroid 
hormone in the intestinal lumen. The goal of this study was to examine the acute 
effects of three previously unstudied medications on levothyroxine absorption.
DESIGN: We studied the effects of three medications on thyroxine absorption in 
seven normal volunteers. On each study day, the subjects ingested 1 mg 
levothyroxine sodium, either taken separately or co-administered with sevelamer 
hydrochloride (Renagel, a phosphate-binding medication used in the treatment of 
hyperphosphatemia), chromium picolinate (an over-the-counter nutritional 
supplement), or ezetimibe (Zetia, a drug used in the treatment of 
hypercholesterolemia). Serum thyroxine was measured at intervals over a 6-hour 
period following drug ingestion.
MAIN OUTCOME: Sevelamer hydrochloride and chromium picolinate each significantly 
(p < 0.05) decreased the area under the serum thyroxine concentration curve, 
while ezetimibe had no effect.
CONCLUSION: Hypothyroid patients taking sevelamer hydrochloride or chromium 
picolinate should be advised to separate the time of ingestion of these drugs 
from their thyroid hormone preparation by several hours.