Greenfield
Adventurer
Cutting through the Bio-101, consider it this way:
The Druid isn't prevented from drinking poison any more than he's prevented from drinking water. He's simply immune to any toxic effects it might have on him.
Medicine might be mildly poisonous to him, hopefully more toxic to whatever disease or parasite it's intended to treat. But he can't be harmed by that toxic effect. The microbe or parasite, however, is certainly susceptible (Unless, of course, it happens to have 9 or more Druid levels.
)
Simpler?
The Druid isn't prevented from drinking poison any more than he's prevented from drinking water. He's simply immune to any toxic effects it might have on him.
Medicine might be mildly poisonous to him, hopefully more toxic to whatever disease or parasite it's intended to treat. But he can't be harmed by that toxic effect. The microbe or parasite, however, is certainly susceptible (Unless, of course, it happens to have 9 or more Druid levels.

Simpler?