If I was given the wrong medication by the pharmacist, what can I do?

Were you injured?  If you were not injured you have no claim.  All claims for malpractice require four elements -- a duty (to fill the prescription accurately), breach of the duty (giving the wrong medication), damages (from an injury), and causation (the breach of duty caused the damages).  If you were injured, I recommend you call a malpractice attorney in your area to see if he or she will represent you.  Not every malpractice attorney handles pharmacy malpractice, but dispensing the wrong medication is clear negligence so you should not have trouble finding a lawyer if you have damages.