Herbs that suppress prisoners' ability to bend their element. This one comes up in a lot of fic, and ... I don't know, the first time I ran across it I just thought, huh, interesting idea, but about the twentieth time, I started wondering if there's some bit of canon to support this that I'm forgetting. Because it strikes me as actively counter to what we saw in the show itself -- there were quite a lot of episodes in which we saw prisoners and prisons, and it was pretty well established how prisoners with *-bending ability are dealt with. Earth- and water-benders are isolated from their element; firebenders are imprisoned in metal cages surrounded by stone walls, so they have nothing to burn (or, in groups, they're guarded by enough firebenders to counter anything they might try to do). For prisoner transport, they bind someone's hands and feet so they can't make the moves required to bend their element.

If they have a chemical way of suppressing bending, shouldn't they have used it at some point rather than using various physical work-arounds?