As per the title, the potion of confusion, when quaffed, is very confusing. To be precise, you will be confused for 8 to 14 turns (blessed), 16 to 22 turns (uncursed) or 24 to 30 turns (cursed).

This potion is much more useful as a projectile weapon. A successful hit on a creature will confuse it for a variable number of turns (this can be resisted by some monsters). Inhaling the vapors confuses you for 1 to 5 turns.

For a more effective and much more "in" method of going through NetHack constantly confused, you should look into the potion of booze and the NetHack Hallucinogens.