Carla, I used the potions and didn't have any problem, so not quite sure what to tell you. You do need to make sure that you're clicking the potion and then clicking on the guy's name, or it won't work. In other words, you can't just click on the character. If that isn't the problem, I don't know.
Where are you in the game? I'm up in the tower after the mirror. But I've spent a lot of extra time fighting, since the baddies reappear every so often.
"How could drops of water know themselves to be a river? Yet the river flows on."
- Antoine de Saint-Exupéry