Loading
Sometimes a strong painkiller has to be changed for another, or given a different way, for example by injection under the skin when swallowing becomes hard. Doses do not swap one for one, so the team works out the new dose from the total taken over 24 hours, often starts a little lower to be safe, and checks closely in the first days.
Switching is considered when pain stays uncontrolled despite an appropriate dose, when side effects are unacceptable (Australian guideline 2025, citing ESMO, NCCN, NICE and ASCO; NICE CG140 1.1.25 for persistent central nervous system effects with uncontrolled pain), or when the oral route is lost. WHO (2018) makes no recommendation for or against switching because no randomised trial has tested it, and presents its conversion tables only as examples. The conversion is done on the total 24-hour dose, looked up in a recognised table or calculator. Ratios in the WHO annex (from the Palliative Care Formulary) include oral to subcutaneous morphine 2:1 and oral morphine to subcutaneous hydromorphone 10:1; oral oxycodone is listed at 1.5 times morphine (manufacturer 2). WHO advises reducing the calculated dose of the new opioid by about 50% when switching at high doses, in older or frail people, because of intolerable side effects such as delirium, or after a rapid recent escalation; the Australian guideline says a dose lower than the equivalent should be used when changing drug. The 2025 MASCC-ASCO-AAHPM-HPNA-NICSO guideline, the first international consensus guideline on conversion, reached agreement on 58 of 84 statements and is described in a 2026 review as challenging traditional dose-reduction protocols; it could be read only as an abstract. Methadone is converted by specialists only.
Why: Many side effects can be treated without changing the painkiller that is working.
“Optimise laxative treatment for managing constipation before considering switching strong opioids.”
NICE 2012 · Not graded (NICE 1.1.20)
Why: People respond differently to different opioids, and another one may give better relief with fewer side effects.
“Optimal pain relief cannot be achieved despite appropriate dose. (ESMO, NCCN, NICE)”
Asia-Pacific Journal of Clinical Oncology 2025 · Adopted from ESMO, NCCN and NICE
Why: Injection under the skin is less painful than into muscle and works when tablets cannot be taken.
“If the oral route is no longer possible, switch to subcutaneous morphine, hydromorphone, oxycodone, or fentanyl. Transdermal fentanyl is another alternative in stable pain.”
Asia-Pacific Journal of Clinical Oncology 2025 · Adopted from source guidelines
Why: Conversion ratios apply to the daily total, and leaving out rescue doses underestimates what the person needs.
“If switching to a different formulation or route of administration with the same agent, look up conversion for total 24‐h opioid dose (ESMO, NCCN, NICE) (e.g., via the eviQ Opioid Conversion Calculator).”
Asia-Pacific Journal of Clinical Oncology 2025 · Adopted from ESMO, NCCN and NICE
Why: Tolerance to one opioid does not fully carry over to another, so an exactly equivalent dose can be too strong.
“If switching to a different agent, a starting dose lower than the equivalent total 24‐h opioid dose of the previous agent should be used.”
Asia-Pacific Journal of Clinical Oncology 2025 · Adopted from source guidelines
Why: These are the situations where an equivalent dose is most likely to cause overdose.
“A dose reduction of around 50% of the calculated equivalent dose of the new opioid is prudent when switching at high doses (e.g. morphine or equivalent doses of ≥ 1 g/24h), in elderly or frail patients, because of intolerable undesirable effects (e.g. delirium), or when there has been a recent rapid escalation of the first opioid (possibly due to opioid-induced hyperalgesia).”
World Health Organization 2018 · Not graded (annex guidance; WHO does not recommend the tables)
Why: Methadone's long and variable action means its effective strength rises with regular use far beyond what a single-dose table suggests.
“P4 Methadone should be initiated and titrated only by specialists familiar with its use. (ESMO, NCCN, ASCO 2016, ASCO 2022)”
Asia-Pacific Journal of Clinical Oncology 2025 · Adopted from ESMO, NCCN and ASCO
Why: Conversion ratios are only approximate and people vary widely, so the new dose is a starting point.
“Thus, careful clinical monitoring during conversion is necessary to avoid under-dosing, excessive dosing and adverse effects, especially when switching at high doses, when rapidly increasing the dose of the first opioid, and when switching to methadone.”
World Health Organization 2018 · Not graded (annex guidance)
How care is usually carried out, read from the guidelines and standards cited. Your own team's protocol and their judgement come first; this page is for understanding it, not for doing it yourself.
Convert on the total 24-hour dose using a recognised table or calculator, start below the calculated equivalent when changing drug, reduce by about 50% in the high-risk situations WHO lists, keep methadone with specialists, and monitor closely afterwards (WHO 2018 annex; Australian guideline 2025 adopting ESMO, NCCN, NICE and ASCO). The evidence is weak throughout: WHO found no randomised trial of switching and makes no recommendation for or against it. The 2025 MASCC-ASCO-AAHPM-HPNA-NICSO guideline is the first international consensus on conversion ratios and, by the account of a 2026 review, questions routine dose reduction; it could be read only as an abstract, so where it differs from WHO and the Australian guideline on the size of the reduction cannot be stated here.
World Health Organization 2018 · Asia-Pacific Journal of Clinical Oncology 2025 · Supportive Care in Cancer 2025 · Journal of Pain and Symptom Management 2026
Where it differs: Reduces the calculated dose of the new opioid by a set percentage on every change of drug, regardless of the reason or dose.
Evidence: WHO reserves its reduction of about 50% for named high-risk situations; the Australian guideline asks for a starting dose below the equivalent without setting a figure. A 2026 review of the MASCC-ASCO-AAHPM-HPNA-NICSO guideline says it challenges traditional dose-reduction protocols; its exact position could not be read.
World Health Organization 2018 · Asia-Pacific Journal of Clinical Oncology 2025 · Journal of Pain and Symptom Management 2026
Where it differs: Some centres convert oral to subcutaneous hydromorphone at 2:1; the manufacturer's ratio in the WHO annex is 3:1. Some centres likewise convert oral to subcutaneous methadone 1:1 rather than 2:1.
Evidence: WHO annex notes, based on mean oral bioavailability (hydromorphone 50%, range 35 to 60%; methadone 80%, range 40 to 100%). No trial.
Where it differs: Uses an online conversion calculator, such as eviQ's in Australia, rather than a printed table.
Evidence: Named by the Australian guideline as the reference for its dose equivalences. A calculator is only as good as the ratios built into it; studies of calculators were not read.
| Recommendation | Grade, as printed | Source |
|---|---|---|
| Opioid switching or rotation “In the absence of evidence, WHO makes no recommendation for or against the practice of opioid switching or rotation.” | No recommendation | World Health Organization 2018 |
| Conversion tables are examples to inform judgement, not WHO recommendations “They are presented merely as examples and should not be construed as recommended by WHO.” | Not graded (annex) | World Health Organization 2018 |
| Consensus reached on conversion statements “In consensus voting, 58 of 84 statements met or exceeded the required 75% level of agreement and were accepted.” | 58 of 84 statements met the 75% agreement threshold | Supportive Care in Cancer 2025 |
| Strength of the evidence behind conversion “The strength of the evidence from the trials is modest, and there are large clinical practice and research gaps.” | Modest (as stated by the panel) | Supportive Care in Cancer 2025 |
| Switch opioid for persistent or moderate to severe central nervous system effects when pain is not controlled “consider switching opioids if pain is not controlled.” | Not graded (NICE 1.1.25) | NICE 2012 |
Shares Fentanyl (transmucosal, for breakthrough cancer pain), Cancer pain management.
Shares Fentanyl (transmucosal, for breakthrough cancer pain), Cancer pain management.
Shares Syringe pumps and subcutaneous syringe drivers, Cancer pain management.
Shares Cancer pain management.
Shares Fentanyl (transmucosal, for breakthrough cancer pain), Cancer pain management.
Shares Cancer pain management.