The doctor gave me a PRESCRIPTION. I took it to the pharmacy, got the medicine, paid the bill, and the pharmacist gave me a RECEIPT. Da dah !

You get a prescription when you go to the doctors.

"Prescription" is correct. "Receipt" is the piece of paper you get from a store to show what you bought. This can be confusing, because in some language (like German) the word for a prescription is "das Rezept," which sounds like "receipt."

ALWAYS "prescription." NEVER "receipt." Sometimes, informally, a prescription is called a "script." And sometimes it's referred to by the abbreviation "Rx." In U.S. English there is an OUTDATED meaning of the word "receipt" to mean a COOKING recipe. I see that ahdictionary.org gives it as the fourth meaning for "receipt." It also says that "receipt" is from a medieval Latin word "receta" which means BOTH a medical prescription AND money received. So the history of the word "receipt" is tangled.