The M367 pill is a white oblong tablet containing hydrocodone 10mg/acetaminophen 325mg — the generic equivalent of Norco 10/325, manufactured by Mallinckrodt and classified as a DEA Schedule II controlled substance. It works by activating mu-opioid receptors to relieve moderate-to-severe pain, but carries serious risks including dependence, respiratory depression, and a critical counterfeit warning: DEA has confirmed fake M367 tablets containing lethal doses of illicitly manufactured fentanyl that are visually indistinguishable from the real pill.
What Is the M367 Pill? Hydrocodone/Acetaminophen Identification
The M367 pill is a white oblong tablet containing hydrocodone bitartrate 10mg combined with acetaminophen 325mg, manufactured by Mallinckrodt Pharmaceuticals. The "M" stamped into the tablet is Mallinckrodt's standard manufacturer identifier, used across their line of generic controlled substance products. This pill is a generic equivalent of Norco 10/325 and is among the most searched opioid imprints in the United States — both because of the widespread historic prescribing of hydrocodone combination products and because of serious counterfeiting concerns that have emerged in recent years.
⚠ DEA SCHEDULE II CONTROLLED SUBSTANCE — Hydrocodone combination products were reclassified to Schedule II in October 2014. Schedule II drugs have a high potential for abuse and may lead to severe physical or psychological dependence. A valid written prescription is required for every fill. Possession without a prescription is a federal offense. This medication may never be legally shared or transferred to another person.
About Mallinckrodt and the "M" Imprint
Mallinckrodt Pharmaceuticals is one of the oldest pharmaceutical manufacturers in the United States, with roots going back to 1867 as a chemical company in St. Louis, Missouri. It became one of the major generic manufacturers of opioid analgesics in the country. The stylized "M" on tablets like M367 is the company's logo imprint, which appears on many of their products — M30 (oxycodone 30mg), M523 (oxycodone/acetaminophen), and others all carry this same identifier.
Mallinckrodt became the subject of significant legal scrutiny in connection with the opioid crisis. In 2020, the company filed for Chapter 11 bankruptcy protection in part due to liabilities related to opioid litigation, and reached a settlement valued at over $1.6 billion with state attorneys general and plaintiffs related to the marketing and distribution of opioids. The company emerged from bankruptcy in 2021 and again filed for bankruptcy in 2023 amid ongoing settlement pressures.
Drug Class and Mechanism of Action
The M367 tablet combines two pharmacologically distinct analgesic agents:
Hydrocodone — Opioid Analgesic
Hydrocodone is a semi-synthetic opioid derived from the natural opioid alkaloid codeine. As a full agonist at mu-opioid receptors (MOR), hydrocodone engages the brain's endogenous opioid system — the same network activated by the body's own endorphins — but with much greater potency and duration. Mu-opioid receptor activation in the periaqueductal gray matter, spinal cord dorsal horn, and other pain-processing regions produces analgesia by inhibiting the transmission of pain signals. These receptors are also responsible for the drug's euphoric and sedating effects, its suppression of respiratory drive at high doses, and the physical dependence that develops with regular use.
Hydrocodone is primarily metabolized in the liver. The CYP2D6 enzyme converts a fraction of hydrocodone to hydromorphone, which is itself a potent opioid and contributes to the drug's overall effect. The CYP3A4 enzyme converts hydrocodone to norhydrocodone, a less active metabolite. Genetic variability in CYP2D6 ("poor metabolizers" vs. "ultra-rapid metabolizers") can significantly affect how individuals respond to hydrocodone.
Acetaminophen — Analgesic and Antipyretic
The 325mg of acetaminophen in M367 provides supplemental analgesia through central nervous system mechanisms. The combination exploits a well-established pharmacological principle: pairing an opioid with a non-opioid analgesic produces additive pain relief, allowing a lower opioid dose to achieve the same clinical effect. This concept — opioid sparing — was a key rationale for combination products, though it must be balanced against the hepatotoxicity risk that acetaminophen carries at elevated intakes.
What Is This Medication Prescribed For?
Hydrocodone/acetaminophen 10mg/325mg is prescribed for moderate to moderately severe pain that is not adequately managed by non-opioid analgesics. This includes acute pain from injury or surgery, dental procedures, and in some cases, pain associated with chronic conditions where opioid therapy has been deemed appropriate after thorough evaluation of risks and benefits. Prescribing of hydrocodone combination products has declined considerably since the 2014 rescheduling and as clinical guidelines have shifted toward multimodal, opioid-minimizing approaches to pain management.
Side Effects and Risks
Opioid-Related Effects
- Sedation and cognitive impairment: Drowsiness, slowed thinking, and impaired coordination are common, especially early in treatment or when doses change. Do not drive or operate heavy machinery.
- Nausea and vomiting: Among the most frequently reported side effects, particularly with first use. Often decreases as tolerance to this effect develops.
- Constipation: A near-universal opioid side effect caused by opioid receptors in the gastrointestinal tract slowing intestinal motility. Unlike many other opioid side effects, tolerance to constipation does not develop meaningfully with long-term use.
- Respiratory depression: The primary mechanism of opioid overdose. Risk is heightened by concurrent use of CNS depressants such as benzodiazepines, alcohol, muscle relaxants, or other opioids. The combination of opioids and benzodiazepines is associated with a disproportionate share of overdose fatalities.
- Physical dependence: With regular opioid use, the nervous system adapts. Abrupt discontinuation or large dose reductions cause withdrawal symptoms including anxiety, muscle aches, sweating, nausea, and insomnia. Dependence is a predictable physiological response, not the same as addiction.
Acetaminophen-Related Risk: Hepatotoxicity
Acetaminophen is the leading cause of acute liver failure in the United States. While 325mg per tablet is a relatively modest amount, cumulative intake from multiple sources must be tracked carefully. Patients taking M367 who also use OTC Tylenol, cold and flu medications containing acetaminophen, or other combination pain products risk exceeding the safe daily intake threshold. Alcohol use dramatically potentiates acetaminophen hepatotoxicity. People with liver disease should use acetaminophen-containing products only under medical supervision.
What to Do If You Find an M367 Tablet
Finding an unidentified white oblong pill stamped M367 is a straightforward identification — but it comes with serious safety considerations:
- Do not take it without a valid prescription. Hydrocodone is a Schedule II controlled substance. Self-administering it without medical oversight is both illegal and dangerous.
- Do not share it. Transferring a Schedule II controlled substance to another person, even informally, is a federal crime regardless of intent.
- Dispose of it properly. DEA-authorized take-back locations and pharmacy drop boxes are the safest disposal method. If no take-back option is available, the FDA has specific guidance for mixing pills with undesirable substances (like coffee grounds) before discarding in household trash. Do not flush unless specifically indicated.
⚠ CRITICAL COUNTERFEIT WARNING — The M367 imprint has been replicated in counterfeit tablets that contain illicitly manufactured fentanyl. DEA laboratory analysis has confirmed that counterfeit pills mimicking common hydrocodone imprints — including M367 — have been seized in large quantities and may contain lethal fentanyl doses. There is no visual method to distinguish a genuine pharmaceutical tablet from a counterfeit one. Pills obtained outside of a licensed pharmacy cannot be assumed to contain what their imprint suggests. Even a single counterfeit fentanyl-laced pill can cause fatal overdose. Naloxone (Narcan) is available without prescription at most U.S. pharmacies and can reverse opioid overdose — consider keeping it accessible.
Frequently Asked Questions
What is the M367 pill?
The M367 pill is a white oblong tablet containing hydrocodone bitartrate 10mg and acetaminophen 325mg — the generic equivalent of Norco 10/325 — manufactured by Mallinckrodt Pharmaceuticals. It is a Schedule II controlled substance used for moderate to severe pain. The combination of hydrocodone (an opioid) and acetaminophen (a non-opioid analgesic) provides enhanced pain relief through complementary mechanisms.
Does the M367 contain acetaminophen (Tylenol)?
Yes. Each M367 tablet contains 325mg of acetaminophen in addition to 10mg of hydrocodone. This means patients must track all other sources of acetaminophen — OTC Tylenol, cold medicines, sleep aids, and other prescription pain products — to avoid exceeding the daily acetaminophen maximum. Excessive acetaminophen is the leading cause of acute liver failure in the United States.
Are there counterfeit M367 pills?
Yes. The DEA has specifically documented counterfeit M367 tablets containing illicitly manufactured fentanyl — drugs that are visually indistinguishable from the legitimate pharmaceutical product. Fentanyl is dramatically more potent than hydrocodone by weight, and a counterfeit M367 tablet can contain a lethal fentanyl dose. Pills obtained anywhere other than a licensed pharmacy filling a valid prescription cannot be verified as safe, regardless of appearance.
What are the signs that someone is having a hydrocodone overdose?
Hydrocodone overdose produces the classic opioid toxidrome: extreme sedation or inability to be woken up, very slow or stopped breathing, pinpoint pupils, and bluish or grayish discoloration of the lips or fingertips (cyanosis) indicating oxygen deprivation. This is a life-threatening emergency requiring immediate 911 contact. If naloxone (Narcan) is available, administer it — it reverses opioid-induced respiratory depression rapidly and is available without a prescription at most U.S. pharmacies.
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