Pharmacology · Opioids and antagonists
Butorphanol !
An opioid agonist-antagonist: a partial μ agonist and a full κ agonist. It has a respiratory ceiling but can cause dysphoria and withdrawal.
Updated 2026-11-01
The figure shows morphine in the μ receptor; butorphanol occupies the same site. There is no structure of butorphanol in an opioid receptor.
Mechanism of action
Butorphanol is a partial μ-receptor agonist and a full κ-receptor agonist. κ activation adds to analgesia and sedation, but also to psychotomimetic effects and dysphoria. As a partial μ agonist it antagonises full agonists and can precipitate withdrawal in dependent patients.
- Fully activates the κ receptor
- Only partly activates the μ receptor
- Pain relief and sedation with a ceiling on breathing
- κ activation can cause dysphoria and hallucinations
Pharmacokinetics
- Absorption
- Injection or nasal spray.
- Metabolism
- Liver, to hydroxybutorphanol; its half-life triples in hepatic impairment.
- Elimination
- Kidney; its half-life doubles in severe renal impairment.
Indications
- Pain needing an opioid, including labour pain
- Pre-anaesthetic medication and supplement to anaesthesia
Adverse effects
Common
- Drowsiness and dizziness
- Nausea and vomiting
- Psychotomimetic effects (dysphoria, hallucinations)
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: dysphoria or hallucinations
- Blood pressure
Administration and safety
- Used with caution in acute myocardial infarction, ventricular dysfunction or coronary insufficiency, because it increases cardiac workload.
- In kidney or liver disease the dosing intervals are lengthened.
- 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.
- Ask about opioid use: it can precipitate withdrawal.
- Watch for confusion, dysphoria or hallucinations.
Pregnancy and breastfeeding
It crosses the placenta; it is used in labour and the newborn is watched for respiratory depression.
Test yourself
Think of the answer, then tap the question to see it.
Why can butorphanol cause dysphoria and hallucinations?
Because it is a full κ-receptor agonist, and κ activation produces psychotomimetic effects.
Why is it used with caution in acute myocardial infarction?
Because it raises pulmonary artery pressure, vascular resistance and cardiac workload.
What happens if butorphanol is given to a morphine-dependent patient?
As a partial μ agonist it can displace morphine and precipitate withdrawal.
Related drugs
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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: Butorphanol Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); BUTORPHANOL TARTRATE injection, solution (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.