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Pharmacology · Opioids and antagonists

Pentazocine !

A partial μ and κ-agonist opioid. By mouth it is combined with naloxone to prevent injection misuse; at high doses it causes dysphoria.

Updated 2026-11-01

The figure shows morphine in the μ receptor; pentazocine occupies the same site. The only available pentazocine structure is in the sigma-1 receptor, which is not its analgesic target.

Target in 3D: κ (agonist) and μ (partial agonist) opioid receptors. PDB structure 8EF6 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Pentazocine is a partial μ-receptor agonist and a κ-receptor agonist. It produces pain relief, sedation and respiratory depression with a ceiling effect; at high doses κ activation causes dysphoria and psychotomimetic effects. Tablets combine it with naloxone: by mouth naloxone hardly acts, but if the product is injected it blocks pentazocine's effect.

  1. Partly activates the μ receptor and activates the κ receptor
  2. Pain relief with a ceiling on breathing
  3. At high doses κ activation causes dysphoria
  4. The tablet's naloxone acts only if injected: it deters misuse

Pharmacokinetics

Absorption
By mouth, combined with naloxone.

Indications

  • Pain needing an opioid when other options are not enough

Adverse effects

Common

  • Dizziness and drowsiness
  • Nausea and vomiting
  • Dysphoria and hallucinations at high doses

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

Benzodiazepines, alcohol and other central nervous system depressants
Add up to profound sedation, respiratory depression, coma and death.
Full μ agonists (morphine, fentanyl) in use or dependence
Can weaken their pain relief and precipitate withdrawal in dependent patients.

What is monitored

  • Respiratory rate and sedation
  • Mental state

Administration and safety

  • The tablet contains naloxone to prevent injection use; it is not dissolved or injected.
  • 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.
  • Watch for confusion, dysphoria or hallucinations.
  • Ask about other opioid use: it can precipitate withdrawal.

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.

Why do pentazocine tablets contain naloxone?

To prevent misuse by injection: by mouth naloxone hardly acts, but injected it blocks pentazocine's effect.

Which receptor explains pentazocine's dysphoria at high doses?

The κ receptor, at which it is an agonist.

What kind of action does pentazocine have at the μ receptor?

It is a partial agonist, with a ceiling for pain relief and respiratory depression.

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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: Pentazocine and Naloxone: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); PENTAZOCINE AND NALOXONE 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.