So I bought the Dr. Lockhearts Amoryl Cream and I clicked "Use Medicin", but I'm still a zombie. Shouldn't I have turned into a human or did I misunderstand something?

Those are fake cures. :( They always release fake cures before the real one, Dr. Lockheart is a con artist. I'm sorry. The real one is made by using candy hearts at Louis L'Amour's thing. That hasn't been released yet. There's a new cure for each year.

You'll need 50 hearts, when it finally becomes available.

I feel kinda cheated now :/ But thanks a lot for helping me

When in doubt, especially with a large-expense item (as that tends to be for new players), I would suggest you ALWAYS read the news comments before jumping in feet first. It offers usually enough clarity to point to the truth of something, or if it at least plants the seed of doubt, you can come ask on the forums before you do something you may regret :)

Real cures /should/ be soon coming, though!