Something I noted during the playtest was that it seemed incredibly easy to make a build that could regen tank infinitely. It was easy to generate a new elixir in less than the 15 seconds it took for the first one you drank to wear off.
I feel like a good way to combat this would be to make elixirs toxic in high short-term doses. Make drinking consecutive elixirs a dangerous gamble as to whether you will end the fight before the toxic effects become too severe to handle and you fall.
Perhaps as your toxicity goes up your healing slows down, or maybe it lowers your max HP like fallout 4's radiation, or debuffs your armor rating, or any combination of these.