And the worst that can happen if you declare it is that they will confiscate the medication. No fines, etc.
If you don't declare it (even if you have the documentation), the penalties can be quite severe.
If your medication is confiscated, then you can always see a doctor in Australia to obtain different medication. Doctors fees aren't too bad in Australia. It might cost you about $60 or so (unsubsidised).
The cost of the replacement medication however is a different matter (could be reasonable, could be exhorbitant).
Evan :->