adjective. Capable of being used as a substitute, valid as a replacement or alternate item.

adjective. Capable of being substituted.

adjective. capable of being exchanged for another or for something else that is equivalent

adjective. (of words) interchangeable in a given context without changing the import of the expression

"Generics companies will need to do that if they want the FDA to deem their product " substitutable " for the original, meaning that a pharmacist could dispense the copy even if a patient had a prescription for Advair."

nonsubstitutable  unsubstitutable  

exchangeable  synonymous