M366 pill – Tablet-Capsule imprint, strength, color, size, shape, drug class, side effects

What is M366 pill?

M366 is an imprint on a pill identified as white in an elliptical/oval shape. Pill is a combination of two active ingredients acetaminophen 325mg and hydrocodone bitartrate 7.5 mg. This two active ingredient combination pill is used to relieve moderate to severe pain. It contains an opioid (narcotic) pain reliever (hydrocodone) and a non-opioid pain reliever (acetaminophen). It is supplied by Mallinckrodt Pharmaceuticals.

How long does it take for m366 to kick in?

Imprint: M366

Strength: 325 mg / 7.5 mg

Color: White

Size: 15.00 mm

Shape: Elliptical / Oval

Availability: Prescription only

Drug Class: Narcotic analgesic combinations

Pregnancy Category: C – Risk cannot be ruled out

CSA Schedule: 2 – High potential for abuse

Labeler / Supplier: Mallinckrodt Pharmaceuticals

Inactive Ingredients: crospovidone, magnesium stearate, microcrystalline cellulose, povidone, corn starch, silicon dioxide, stearic acid

Active ingredients of M366 pill and their identification

Hydrocodone belongs to the pharmacological class of opioid analgesic and occurs as fine, white crystals or as a crystalline powder.

Acetaminophe or paracetamol is a slightly bitter, white, odorless, crystalline powder, categorized as a non-opiate, non-salicylate analgesic and antipyretic.

M366 chemistry

M366 pill is a combination of two active ingredients: acetaminophen and hydrocodone.


IUPAC name: N-(4-hydroxyphenyl)ethanamide

Molecular formula: C8H9NO2

Molecular weight: 151.163 g/mol

Molecular structure:

M366 chemistry

Drug class: This compound belongs to the class of organic compounds known as 1-hydroxy-2-unsubstituted benzenoids. These are phenols that a unsubstituted at the 2-position.


IUPAC name: 4,5α-epoxy-3-methoxy-17-methylmorphinan-6-one

Molecular formula: C18H21NO3

Molecular weight: 299.368 g/mol

Molecular structure:

What Are M366 Pills? Name, Dosages, and Effects

Drug class: This compound belongs to the class of organic compounds named morphinans, which are polycyclic compounds with a four-ring skeleton with three condensed six-member rings forming a partially hydrogenated phenanthrene moiety, one of which is aromatic while the two others are alicyclic.

M366 mechanism of action

Hydrocodone works as a weak agonist of opiate receptors OP1, OP2, and OP3 within the CNS. This drug primarily affects OP3 receptors coupled with G-protein and function as modulators, both positive and negative, of synaptic transmission via G-proteins that activate effector proteins. After binding to its receptors it stimulates the exchange of GTP for GDP on the G-protein complex.

Effector system is adenylate cyclase and cAMP placed at the inner surface of the plasma membrane. Activation of this effector system decreases intracellular cAMP by inhibiting adenylate cyclase. Consequently, nociceptive neurotransmitters including GABA, substance P, dopamine, acetylcholine, and noradrenaline release is inhibited.

Hydrocodone may also inhibit the release of vasopressin, insulin, somatostatin, and glucagon. Opioids may also close N-type voltage-operated calcium channels (OP2-receptor agonist) and open calcium-dependent inwardly rectifying potassium channels (OP3 and OP1 receptor agonist), resulting in hyperpolarization and reduced neuronal excitability.

Acetaminophen belongs to the group of weaker analgesics. It is suggested that this drug acts primarily in the CNS, where it increases the pain threshold inhibiting both isoforms of enzyme cyclooxygenase, COX-1, COX-2, and COX-3 involved in prostaglandin (PG) synthesis. Differently, from other NSAIDs, acetaminophen does not inhibit COX in peripheral tissues and, thus, has no peripheral anti-inflammatory affects.

Studies also found that acetaminophen selectively blocks a variant of the COX enzyme that is different from the known variants COX-1 and COX-2 which is now referred to as COX-3. However, its exact mechanism of action is still poorly understood. Acetaminophen’s antipyretic properties are most likely due to direct effects on the heat-regulating centres of the hypothalamus.

M366 pharmacokinetics


  • Absorption and distribution: Hydrocodone oral formulation can be absorbed from the gastrointestinal tract and remain 20-50% bound to plasma proteins
  • Onset of action: The onset of analgesia is about 20 to 30 minutes with duration of 4 to 8 hours and t1/2of 3 to 4 hours.
  • Metabolism and excretion: Hydrocodone is metabolized to norhydrocodone by cytochrome P450 3A4 and to hydromorphone, also biologically active, by cytochrome P450 2D6. For patients who have a defect in the gene encoding CYP2D6, the clearance of the drug will be lower and less metabolite such as hydromorphone will be formed; however, the effect on analgesia remains unknown.


  • Absorption and distribution: Acetaminophens’ the half-life of oral acetaminophen is 1.25 to 3 hours and peak level is reached by 10–60 minutes after ingestion.
  • Metabolism and excretion: Acetaminophen is primarily metabolized in the liver through metabolic reactions of glucuronidation and sulfation to mostly non-toxic metabolites and some highly reactive metabolites, which are inactivated by glutathione. 85% of the dose is excreted renally. At high doses, the supply of glutathione cannot meet its demand, thus results in the accumulation of highly reactive compounds may lead to liver damage.

M366 pill uses?

Acetaminophen/hydrocodone is used in the treatment of moderate to severe pain including back pain, severe pain and rheumatoid arthritis. It is also used for the symptomatic relief of nonproductive cough, alone or in combination with other antitussives or expectorants.

M366 legal status

Acetaminophen/hydrocodone 325 mg/7.5 mg is categorized as a Schedule 2 controlled substance under the Controlled Substance Act (CSA). This means that this drug has a high potential for abuse. It has a currently accepted medical use in treatment in the US or a currently accepted medical use with severe restrictions. Abuse of the drug may lead to severe psychological or physical dependence.

What are different brand names for hydrocodone/acetaminophen?

Different brand names for hydrocodone/acetaminophen are: Vicodin, Lorcet, Lortab, Norco, Xodol, Hycet.

M366 price and prescription

Generic hydrocodone/acetaminophen is covered by most Medicare and insurance plans, but some pharmacy coupons or cash prices may be lower. The lowest price by GoodRx for the most common version of hydrocodone/acetaminophen is around $14.70, 72% off the average retail price of $52.81.

M366 side effects

Acetaminophen/hydrocodone may cause following side effects:

Common side effects:

  • Drowsiness
  • Dizziness
  • Nausea, vomiting
  • Constipation

Serious side effects:

  • Difficulty with breathing, allergy and swelling of the face, lips, tongue or hives
  • Decreased breathing, bradycardia
  • Lightheadedness
  • Convulsions
  • Feeling anxious, fearful, or depressed; mood swings
  • Confusion, unusual thoughts
  • Difficulty urinating
  • Upper abdominal pain, itching, little appetite, dark urine, clay-colored stools, jaundice
  • Skin redness or rash that causes blistering

Can M366 cause dependence?

Hydrocodone may become habit-forming when it is used for a long-time period, causing mental or physical dependence. However, patients who have continuing pain should not let the fear of dependence keep them away from using narcotics to relieve their pain. Mental dependence (addiction) is not likely to occur when hydrocodone is used for this purpose.

There is also a chance for physical dependence after hydrocodone long-term use to occur which may lead to withdrawal side effects if drug therapy is stopped suddenly. But, severe withdrawal side effects can usually be prevented by gradually reducing the dose over a period of time before treatment is stopped completely.

Can you take hydrocodone and tramadol at the same time?