It's always bad if you think about these things but here goes .........
The
Incoming Passenger Card just asks you to declare
Goods that may be prohibited or subject to restrictions, such as
medicines, steroids, firearms, weapons of any kind or illicit drugs?
As the specific medicines are not prohibited or subject to restrictions as they are neither on the government list and I have a signed doctor's prescription - surely the answer to this question is "No"?
EDITED TO ADD (TO HELP OTHERS!)
Answered my own question:
Medicinal products
Declare all drugs and medicines including prescription medications,
alternative, herbal and traditional medicines, vitamin and mineral
preparations and performance-enhancing drugs or formulas.
Travellers Guide Page 7