A potion of extra healing will heal you when you quaff it. A blessed one heals 8d8 HP, an uncursed one 6d8 HP, and a cursed one 4d8 HP. If this would bring your HP above its maximum, your maximum will increase by 2 for an uncursed potion, or 5 for a blessed potion. The potion will also cure hallucination and blindness, exercise constitution and strength, and, if noncursed, cure sickness.
Dipping a poisoned weapon into a potion of extra healing will remove the poison and use up the potion.
You can throw this potion at Pestilence or hit him with it to damage him and reduce his maximum HP.
Monsters know how to use these, and shopkeepers may be generated with one.
Some players, especially pacifists or protection runners, quaff this potion right away for the maximum HP boost.