A new study has found that the drug Renagel (sevelamer hydrochloride), which is used to control phosphorus levels in patients with chronic kidney disease, can interfere with the absorption of the thyroid medication levothyroxine (i.e., Synthroid, Levoxyl, Levothroid). Based on the results of the study, reported in the journal Thyroid, researchers are recommending that patients taking Renagel and thyroid hormone replacement be sure to take these medications separately, at least 2 to 3 hours apart.

_{Source: John-Kalarickal, Jennifer et. al. New Medications Which Decrease Levothyroxine Absorption, Thyroid. 2007, 17(8): 763-765. doi:10.1089/thy.2007.0060.}