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M523 is a generic prescription medicine used to treat moderate to severe pain. It is white in color, oblong shaped, measuring 16mm in size.

They are listed as a Schedule II controlled substance, meaning there is a high potential for misuse, abuse and addiction. Their drug classification is narcotic analgesic, combining the effects of a strong opioid and a non-opioid medication.


  • Oxycodone hydrochloride 10 mg
  • Acetaminophen 325 mg
both sides of M523 pill

Oxycodone is a potent, full opioid agonist which modulates pain perception and response. On the other hand, acetaminophen works primarily in the central nervous system to inhibit synthesis, thereby reducing pain and fever. Together, these two compounds create a potentiating effect that enhances the analgesic action, thereby reducing pain more effectively than either ingredient could on its own.

After oral administration, oxycodone is well absorbed from the gastrointestinal tract and extensively metabolized in the liver to produce metabolites, including noroxycodone, oxymorphone, and noroxymorphone.

  • The half-life varies from person to person, typically between 3 to 5 hours.

Side Effects

It is essential to be aware of this medication’s potential side effects. They can include:

  • Drowsiness
  • Dizziness
  • Nausea or vomiting
  • Constipation
  • Headache
  • Dry mouth
  • Sweating
  • Itching
  • Lightheadedness
  • Weakness or fatigue

For further, more detailed information, see box warnings.

Dependency Risk

The risk of addiction, abuse, and misuse is very high as it contains oxycodone, an opioid agonist. Long-term use can lead to physical dependence and withdrawal symptoms upon cessation. Overdosing can lead to life-threatening respiratory depression and death.

  • Pregnant women should avoid using this medication due to potential risks to the fetus.


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IngredientsOxycodone hydrochloride (10 mg), Acetaminophen (325 mg)
IndicationsManagement of moderate to severe pain
ContraindicationsAsthma; opioid or acetaminophen sensitivity
Drug ClassNarcotic analgesic
AvailabilityPrescription only
MarkingsAlpha-numbers on one side, ingredients on other
ClassificationSchedule 2 controlled substance
Mechanism of ActionOxycodone is a full opioid agonist with relative selectivity for the mu-opioid receptor
StorageDark, cool
Pregnancy RiskRisk
FDA ApprovalYes
SupplierMallinckrodt Inc.

See a side-by-side comparison between Xanax and Etizolam, here.