There is no all-encompassing list of 'banned' medications publically available for Australia. In the regulations there is a 'catch all' to the effect of "pilots must not take any medications which may inhibit their ability to fly safely".
If you want specific advice on a specific medication, why not give CASA a call? That or you can see a DAME (which is a GP qualified to do aviation medical assessments).
What you can find out there is general advice though. Although questions such as this on ADHD and this more generally refer to the US system, the Australian restrictions are not too dissimilar.
Broardly speaking, Ritalin and other 'depressants' are incompatible with flying. Bi-polar disorder faces many restrictions but stable depression is manageable. I did hear somewhere that you need to be off antidepressants for 12 months though. Diabetes and blood thinning medications are OK but subject to regular testing and scrutiny.
As an aside, sometimes CASA, instead of outright refusing the medical, will place restrictions on it instead. This can be things like you must fly by day VFR only, or you can only fly with a qualified pilot next to you.
EDIT: I found this page from the CASA website which has a list of medications to stay away from. It's not exhaustive but it's a start