Some drugs may inhibit iron absorption, and iron can, in turn, inhibit absorption of some drugs. Here are a few examples, but remember to refer to standard compendia (eg. national formularies) for further information.
Drugs that may inhibit iron absorption:
Magnesium salts
Tetracyclines
Trientine
Zinc
Drugs whose absorption can be inhibited by iron:
Bisposphonates
Ciproflaxacin
Entacapone
Levodopa
Penicillamine