The white/ oval pill imprint with m366 has been identified as Acetaminophen and Hydrocodone Bitartrate 325 mg / 7.5 mg. M366 pills are meant to be used to relieve moderate to severe pain. They’re typically prescribed by your doctor to give you relief from short-term pain. For example, if you just had back surgery, then your doctor might prescribe you M366 pills to help you with the pain from surgery. However, they’re not usually given to patients with long-term pain (such as ongoing back pain) because they can be addictive.