APB11,
Give CASA medical a call and speak to Georgie, She is amazing. I personally and a few of my colleagues have used her throughout our complicated processes and her assistance has been invaluable! Ask specifically how long after completion of taking the medicine before you will be eligible for your medical? What clearance documentation will they require?
Preferably get it in writing!!!
With a lot of medicine on the do not take list, you can finish taking it and get your medical a few days later (with the appropriately worded clearance from your doctor). Otherwise, there are some (don't ask me the name... can't remember) that can be a period of 6 months after taking before you are cleared.
As for ASA, I can only go off what I have read. My assumption is that if you are unable to ascertain your medical within the required time and you inform them they "should" delay you for a later course.
Best of luck mate, and if you need some help with CASA medical feel free to PM me, I may not be able to do much but you never know!