Why must prescriptions be written in ink?

It’s a common misconception that prescriptions must be written in ink. There is no such mandate from any regulatory agency – they only say prescriptions _be legible._ So even pencil works if it’s legible. Even the use of an indelible pen isn't always a good idea: if the doctor makes corrections, any pen or eraser might be considered as "changing the substance of the prescription in any manner”--something many states forbid