Not Medical Advice: The white pill with "M366" imprinted on it is Acetaminophen and hydrocodone bitartrate. The dosage is 325 milligrams of Acetaminophen and 7.5 milligrams of hydrocodone bitartrate. It's a mixture of two pain medications, and is in the drug class known as narcotic analgesic combinations.
It's mainly used to treat pain and back pain, but is also commonly used to treat rheumatoid arthritis. A less common usage is in the treatment of a cough.
Because it contains Acetaminophen, this medication can be harmful to the liver. Due to this, it's recommended not to exceed 4,000 milligrams of Acetaminophen per day, which would be about 12 pills. The drug does have a moderate potential for abuse, so it is a prescription only medication.
It's not recommended to combine it with other depressants, other pain relievers, alcohol, or allergy/cough medications.