the only way you can fix diseases in its current form is to ensure you have about 1:4 medicine to regular drinks. should give u enough coverage to not get sick. alternatively one could edit all alcohol to be medicine.
you could also "cheat" and just make medicine require 1 plant vs two, and only make medicine.
Or maybe give 3 medicine drinks for every 2 plants. Or 5 for every 3 plants to help alleviate. edit: I have this backwards, 3 plants produce 2 medicine, or 5 plants for 4 medicine.
I think I really like that idea, I always struggle with the # of drinks (as sick dwarves tend to prevent me from ever reaching full capacity),
so something like 3 drinks for every 2 plants 2 to 3 would help as it would increase the # of medicine by 50%. Even then, I still think I would struggle with enough medicine.
I find that I need to build about 2 to 4 times more farms than normal (in it's current state) to produce enough drinks after 4 years, but the most I've built is only about 2 times larger and I never really had a good medicine industry up.
However, I think what Meph has in mind, like an area of effect building that bestows a syndrome of medicine for those nearby it, would help a lot more. Like a vaccination center
update: I'll just add a new product line that has a 50% to produce a 2nd drink
further update:
I see 5 drinks are made with 2 plants... so I guess there's no need for chance changes. However, if plants are stacked higher than 2 (not sure how stacks work, but I know it was a problem with bones)... so I'm thinking plants might be getting shorted due to stacks being pulled to make medicine drinks?
So I just doubled it from 5 to 10I tried this in plant_fake... So now medicine costs 60% of drink production, but is only needed at a fraction of the amount of drinks. I don't remember, I think it's 16 drinks a year, but medicine is only needed 3 times a year.
[REACTION:MAKE_MEDICINE]
[NAME:Make medicine potion from plants]
[BUILDING:APOTHECARIUS:CUSTOM_SHIFT_M]
[REAGENT:A:1:PLANT:NONE:PLANT_MAT:NONE:STRUCTURAL][UNROTTEN][DOES_NOT_DETERMINE_PRODUCT_AMOUNT]
[REAGENT:B:1:NONE:NONE:NONE:NONE]
[EMPTY][FOOD_STORAGE_CONTAINER][PRESERVE_REAGENT][DOES_NOT_DETERMINE_PRODUCT_AMOUNT]
[PRODUCT:100:3:DRINK:NONE:PLANT_MAT:MEDICINE:DRINK][PRODUCT_DIMENSION:150]
[PRODUCT_TO_CONTAINER:B]
[SKILL:DIAGNOSE]