In order to bring a successful claim for a medication error, you will need to show an error on the part of whoever gave you the incorrect medicine, and that you have suffered some form of injury as a result of that error. The injury might only be modest, for example symptoms lasting a few hours. On the other hand, symptoms might be lifelong and have a devastating effect on your life; the effects of giving the wrong medication can also be fatal.
So if, for example, you have been prescribed paracetamol (a common painkiller) instead of atorvastatin (medication for high cholesterol) you may experience symptoms or problems that otherwise would have been kept under control by the atorvastatin. You may be able to bring a claim for medical negligence to recover compensation for those uncontrolled symptoms.