CALCIUM AND MAGNESIUM SALT, INCLUDING ANTACIDS, MINERAL SUPPLEMENTS, BICARBONATES, CARBONATES, OXALATES, OR PHOSPHATES, TEETACYCLINES MAY IMPAIR ABSORPTION OF IRON. ZINC SALT REDUCE ABSORPTION OF IT. IRON RESPONSE MAY BE DELAYED IF USED WITH CHLORAMPHENICOL. IT MAY REDUCE THE EFFICACY OF THYROXINE.