[Varyon]

For Eraser, a potential option (although it would cause a disconnect if changed in the middle of a campaign) would be to get rid of the associated knockout effect and instead simply have it temporarily cause anterograde amnesia, preventing those exposed to it from forming new long-term memories for some amount of time. They'll be able to function well enough to keep fighting, run away, or whatever, but will forget events from several minutes prior (essentially, they'll have a several-minute cache of short-term memory, and will be continuously overwriting the oldest bits instead of shunting them over to long-term memory). Clever ones will realize their memory is failing them and make written/typed backups to help keep things straight, but by the time they realize to do that, they'll likely have already forgotten whatever important thing you needed them to forget. This lets Eraser largely function the way it's meant to (removing problematic memories) without turning it into an "I win" knockout drug. And, yes, much of the above is stolen from a plotline from the webcomic Freefall.

For a bit of dark humor, you could also have it be that because your characters use the stuff so excessively, it has now been discovered Eraser can have serious side-effects, and they can't use it with impunity anymore.