True to its name, this
NetHack potion causes
blindness when
quaffed. The blindness will last from 125 to 575 (or maybe more) turns, which can obviously cause problems. Good
insurance against accidentally quaffing one of these is
telepathy or a
unicorn horn.
This potion can be thrown at monsters to blind them instead. If you inhale the vapors of a smashed potion of blindness, you will be blinded for 1-5 turns.
Additionally, dipping a unicorn horn into this potion will change it into uncursed water.