I do know that when Lacey is on really high doses of Bute (for ERU, she gets 2 grams/day during a flare up) she gets extra "nutty" in a way she does not get on other painkillers. She's not only more active, she's more just...loopy and silly - kinda like what one would associate with a "sloppy" drunk.
Like, she's generally very careful about her personal space, careful where she walks so she doesn't slip or fall, etc, but on bute, she could care less if she bumps into you, falls over, etc. Its just weirddd.
So I would agree with the previous posters and say that there's probably an element of "All pain is gone!! YAHOO!" but there's also the possibility that Bute does literally "mess with his mind" a bit.
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.