What is the name of a large round beige colored pill scored M on one side and PC1 on the other side?

The pill you are describing is likely to be Diphenhydramine Hydrochloride 25 mg, which is an antihistamine commonly used for Allergies and sleep aid. It is beige, round, and scored with an "M" on one side and "PC1" on the other side. However, it is important to verify any medication with a healthcare professional or a reliable source.