Interaction of Generic Synthroid with other medications can render it less effective. For this reason, avoid taking the following medications 4 hours before or after taking Generic Synthroid: calcium carbonate (Caltrate, Citracal, Oystercal, etc.); ferrous sulfate iron supplements; sucralfate (Carafate); sodium polystyrene sulfonate (Kayexalate, Kionex, etc.); aluminum or magnesium antacids (e.g. Acid Gone, Aldroxicon, Alternagel, Di-Gel, Gaviscon, Gelusil, Genaton, Maalox, Maldroxal, Milk of Magnesia, Mintox, Mylagen, Mylanta, Pepcid Complete, Rolaids, Rulox); or medications to lower cholesterol levels such as cholestyramine (Questran) and colestipol (Colestid).