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Pharmacology · Opioids and antagonists

Oxycodone !

A semi-synthetic oral μ agonist for severe pain, alone or combined with paracetamol. Its CYP3A4 metabolism exposes it to dangerous interactions.

Updated 2026-11-01

The figure shows morphine in the μ receptor; oxycodone, a thebaine derivative, occupies the same site. There is no structure of oxycodone in the receptor.

Target in 3D: μ-opioid receptor. PDB structure 8EF6 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Oxycodone is a full μ-receptor agonist derived from thebaine. It activates the Gi protein, inhibits neurotransmitter release in the pain pathway and changes the emotional perception of pain; in the brainstem it depresses breathing and suppresses cough. A small part is converted to oxymorphone, which is also active.

  1. Activates the μ receptor in the spinal cord and brain
  2. The Gi protein reduces release of pain neurotransmitters
  3. Relief of severe pain by mouth
  4. In the brainstem: less drive to breathe, above all with other depressants

Pharmacokinetics

Absorption
Well absorbed by mouth; immediate- and extended-release forms exist.
Metabolism
Liver: much of it is N-dealkylated to noroxycodone by CYP3A4; a smaller fraction is O-demethylated to oxymorphone.
Elimination
Kidney, as metabolites.

Indications

  • Pain severe enough to need an opioid when other options are not enough

Adverse effects

Common

  • Nausea and vomiting
  • Trouble sleeping
  • Headache
  • Weakness and tiredness
  • Lower sexual desire

Contraindications

  • Significant respiratory depression
  • Acute or severe bronchial asthma without monitoring or resuscitation equipment
  • Known or suspected gastrointestinal obstruction, including paralytic ileus
  • Hypersensitivity to the drug

Key interactions

CYP3A4 inhibitors (macrolides, azoles, ritonavir), or stopping inducers (rifampicin, carbamazepine, phenytoin)
Raise opioid levels and can cause a fatal overdose.
Benzodiazepines, alcohol and other central nervous system depressants
Add up to profound sedation, respiratory depression, coma and death.
CYP3A4 inducers, or stopping an inhibitor
Lower its levels: weaker pain relief or withdrawal.

What is monitored

  • Respiratory rate and sedation
  • Bowel habits
  • Signs of misuse

Administration and safety

  • Extended-release forms are swallowed whole; crushing or chewing them releases a potentially fatal dose.
  • Switching from immediate to extended release is not a one-to-one conversion: there is a risk of excessive sedation.
  • Check whether the product contains paracetamol so the total allowed is not exceeded.
  • Controlled medicine: the order is verified, every dose recorded and leftovers kept secure.

Nursing care

  • Before each dose: respiratory rate, oxygen saturation and sedation level; hold the dose and report excessive sedation or slow breathing.
  • Keep naloxone at hand and teach the family to recognise an overdose.
  • Prevent constipation from the start and track bowel habits.
  • Prevent falls: dizziness, drowsiness and orthostatic hypotension.
  • Teach the patient to lock the medicine away and dispose of leftovers safely.

Pregnancy and breastfeeding

Prolonged use in pregnancy can cause neonatal opioid withdrawal syndrome, which is expected and treatable; the newborn is watched after birth.

Test yourself

Think of the answer, then tap the question to see it.

Which enzyme metabolises most oxycodone, and what risk does that carry?

CYP3A4; its inhibitors (macrolides, azoles, ritonavir), or stopping inducers, can cause a fatal overdose.

Why are extended-release oxycodone tablets never crushed?

Because the whole dose is released at once, which can be fatal.

Which active metabolite does a small part of oxycodone form?

Oxymorphone, by O-demethylation.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Oxycodone: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); OXYCODONE HYDROCHLORIDE tablet (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 23 (McGraw Hill, 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.