Digitalis symptoms appropriate to gaming are generally
yellow tint to the vision
tiredness (general weakness - CON)
weakness (decrease in muscle strength - STR)
confusion (trouble understanding the environment - INT or WIS)
dizziness (spinning and unsteady - clearly DEX)
abnormal dreams or nightmares
nausea and vomiting
cramping
loss of appetite (erm, generally from the nausea and cramping? lol)
Long term severe cases can cause death. In modern day terms there is generally a heart medication that is usually the culprit, and dosages are merely changed and monitored to alleviate the symptoms.
Why not do something different with this poison and take some temporary damage against all these stats - maybe a point each? Thats something you generally dont see. While modern day times dont generally see dosages on the level necessary to cause this level of reaction a direct poisoning effort might I suppose. A failed secondary could be the continued progression of lowering stats (perhaps a new save allowed each day to delay progression?)until one or more reach 0, when of course we all know what happens...
I cant begin to imagine what the DC to MAKE it would be, but I would put it AND the price high if it has such drastic results...