You may not quaff potions if you:
- Are a mummy
- Are in Lich Form
- Are berserk
- Have the -Potion status:
- Killer Klowns gained their pie attack in 0.23.
- Ru and its sacrifices were added in 0.16
- Prior to 0.15, Ozocubu's Refrigeration had no impact on your ability to quaff potions (but did occasionally destroy them in your inventory). There was also a retching status that prevented you from quaffing.
- Prior to 0.14, you could quaff from fountains, receiving various effects.