The code stamped into any prescription tablet functions as an unambiguous chemical serial number. An oblong white tablet bearing "M367" on one side and a single bisecting score line on the reverse contains precisely 10 mg of hydrocodone bitartrate paired with 325 mg of acetaminophen. The "M" inside a box or stylized square denotes Mallinckrodt Pharmaceuticals, a major supplier of generic analgesics across North America.
The combination belongs to a class of combination drugs formerly sold under brand names such as Norco 10/325 and Vicodin HP. The hydrocodone component acts directly on mu-opioid receptors within the central nervous system to intercept pain signaling between peripheral nerves and the brain. Acetaminophen works as a non-opioid synergistic agent, inhibiting prostaglandin synthesis in spinal pathways to enhance pain relief without requiring a higher, more hazardous narcotic dose.
Prior to 2014, retail pharmacies dispensed hydrocodone combinations with up to 500 mg or 650 mg of acetaminophen per dose. The U.S. Food and Drug Administration eliminated those elevated ratios after clinical data showed that acetaminophen toxicity accounted for roughly 50% of all acute liver failure cases nationwide. Modern formulations like the M367 tablet cap the non-opioid base at 325 mg to preserve hepatic safety during prolonged treatment plans.
