What is a pale yellow round pill with m89 on it?

A pale yellow round pill imprinted with "M89" is identified as Diphenhydramine Hydrochloride 25 mg, an over-the-counter antihistamine commonly used to relieve symptoms of Allergies, hay fever, and the common cold. It can help alleviate symptoms such as runny nose, sneezing, and itching. Additionally, it is often used as a sleep aid due to its sedative properties. Always consult a healthcare professional before using any medication.