There are 2 problems right now with alchemy:
1. Using two herbs and alchemy a player can have unlimited access to fireballs once he gets proper shielding from the blast effect.
2. With the introduction of "Cold blood" corruption the player can boost his speed up to around 200 before anticipated tough battles. This is done by creating multiple herbal explosions just before the battle.

Both of these effect make the characters seriously overpowered. I was able to clear the whole Earth temple using nothing but herbal explosions. In conjunction with Cold Blood corruption this is particularly game breaking as there are a handful of monsters in the entire game that have their speed above 150 not to mention 200.

SOLUTION:
We discussed a bunch of solutions for this on general forum and the most balanced one is to remove the ability to mix two herbs together. If a player wants to create an explosion he has to sacrifice some potion. The player will be in possession of limited quantity of useless potions contrary to unlimited herbs. Seems clean, simple and easy to implement.