Dose equivalents and changing opioids

  • Switching from one opioid to another should only be recommended or supervised by a healthcare practitioner with adequate competence and sufficient experience. If uncertain, ask for advice from a more experienced practitioner.
  • Opioid rotation or switching may be considered if a patient obtains pain relief with one opioid and is suffering severe adverse effects.
  • When converting from one opioid to another, the initial dose depends on the relative potency of the two drugs and route of administration.
  • An individualised approach is necessary.
  • Conversion factors are an approximate guide only because comprehensive data are lacking and there is significant inter-individual variation.
  • In most cases, when switching between different opioids, the calculated dose-equivalent must be reduced to ensure safety. The starting point for dose reduction from the calculated equi-analgesic dose is around 25-50%.
  • A dose reduction of at least 50% is recommended when switching at high doses (eg, oral morphine or equivalent doses of 500mg/24 hours or more), in elderly or frail patients, or because of intolerable undesirable effects.
  • The half-life and time to onset of action of the two drugs needs to be considered when converting so that the patient does not experience breakthrough pain or receive too much opioid during the conversion period.
  • Once the conversion has occurred, the dose of new opioid should be titrated carefully according to individual response and the patient monitored closely for side effects and efficacy, especially when switching at high doses.
  • Withdrawal symptoms (eg, sweating, yawning and abdominal cramps, restlessness, anxiety) occur if an opioid is stopped/dose reduced abruptly.


Approximate equi-analgesic potencies of opioids for oral administration

(Reviewed August 2020 to reflect current BNF figures)

  Potency  Equivalent dose to 10mg oral morphine
Codeine phosphate 0.1 100mg
Dihydrocodeine 0.1 100mg
Hydromorphone 5 2mg
Methadone * *
Morphine 1 10mg
Oxycodone 1.5 6.6mg
Tapentadol 0.4 25mg
Tramadol 0.1 100mg

* The relative potency of methadone depends on the starting dose and the duration of administration. Conversions to and from methadone should always be undertaken with specialist advice


Transdermal Opioids

(Reviewed August 2020 to reflect current BNF figures)

A. Buprenorphine

Transdermal buprenorphine changed at weekly intervals

  5 microgram/hr 10 microgram/hr 20 microgram/hr
Codeine phosphate (mg/day) 120mg 240mg  
Morphine sulphate (mg/day) 12mg 24mg 48mg


Transdermal buprenorphine changed every three or four days (twice weekly)

  35 microgram/hr 52 microgram/hr 70 microgram/hr
Morphine sulphate (mg/day) 84mg 126mg 168mg


B. Fentanyl

Fentanyl patch strength (microgram/hr) Oral morphine (mg/day)
12 30
25 60
50 120
75 180
100 240



Further Reading

  • British National Formulary.
  • Fine PG, Portenoy RK; Ad Hoc Expert Panel on Evidence Review and Guidelines for Opioid Rotation. Establishing "best practices" for opioid rotation: conclusions of an expert panel. Journal of Pain and Symptom Management 2009 ;38: 418-25.
  • Twycross R, Wilcock A, Howard P. PCF 5Palliative Care Formulary. 2014. 
  • UK Medicines Information. Q&A 42.8 What are the equivalent doses of oral morphine to other oral opioids when used as analgesics in adult palliative care? 2016.
  • Webster LR, Fine PG. Review and critique of opioid rotation practices and associated risks of toxicity. Pain Medicine 2012; 13: 562-70.