What is a dark blue pill with 219 on it?

A dark blue pill with the imprint "219" is identified as Diphenhydramine hydrochloride 25 mg, which is an over-the-counter antihistamine. It is commonly used to relieve symptoms of allergy, hay fever, and the common cold, such as sneezing, runny nose, and itching. Additionally, it can be used as a nighttime sleep aid due to its sedative properties. Always consult a healthcare professional before using any medication.