Final answer:
The pharmacist should contact the physician to verify the prescription for Propecia® written on plain paper.
Step-by-step explanation:
When a pharmacist encounters a prescription for Propecia® written on a plain piece of paper instead of an official prescription blank, the best course of action would typically be to contact the physician to verify the prescription. While a prescription does not necessarily have to be on a specialized blank to be valid, verification is key to ensuring the authenticity of the prescription, especially given the unusual circumstances. In this scenario, choosing to contact the physician upholds the pharmacist's duty to ensure patient safety and medication accuracy.