My DH also has a progressive illness with good days and bad days, and meds that vary according to how ill he is.
As far as I can remember we didn't overtly include the effect of his medication on the DLA form, although we did have to list what his meds are; what we seemed to concentrate on was what a good day means for him, and what a bad day involves. I was advised that when filling in this form it's very important to say exactly what a bad day is, and be as detailed about a bad day as possible. Don't gloss over it, or tone it down. After all, the DLA is there to buy in services you can't supply for yourself: so if you can't go shopping, you can pay someone to do your shopping for you, etc.
My DH felt a bit, well, fraudulent for only saying what his bad days are, which is why we put down both extremes on his form. He was happy doing that, and his application was successful - but of course that's just his experience.
With the form DH had to contact details of his gp and hospital consultant. We assumed they would supply all the info needed for the DLA assessment regarding DH's varying medication, and the effect of said meds.
How are you getting on with the monster form? Good luck 