Short answer: current UK opioid-conversion guidance does not support a simple claim that dihydrocodeine is “twice as strong” as codeine. The Faculty of Pain Medicine places oral codeine phosphate and dihydrocodeine in the same approximate potency range relative to oral morphine, while also warning that opioid conversions are only estimates and individual response can vary.
That means the better question is not only “which is stronger?” but also which medicine is appropriate for the type of pain, formulation, previous treatment response and individual patient. Both medicines are opioids and both can cause drowsiness, constipation, breathing problems, dependence and addiction.
This guide compares dihydrocodeine and codeine for pain relief in the UK, with a focus on strength, how they work, practical differences and safety.
Not in a simple, universal way. The Faculty of Pain Medicine currently lists oral codeine phosphate and oral dihydrocodeine with the same approximate potency factor relative to oral morphine. Its guidance also stresses that conversion figures are approximate, data are limited and there is significant variation between individuals.
This is important because some older resources and patient discussions describe dihydrocodeine as stronger. In practice, however, a fixed statement such as “dihydrocodeine is twice as strong as codeine” is too absolute for patient guidance. Dose, formulation, metabolism, age, other medicines and the reason for treatment can all affect the result.
Codeine also has an important source of variability: its pain-relieving effect depends on conversion to morphine through the liver enzyme CYP2D6. People metabolise codeine differently, so the same dose may not produce the same analgesic effect or side-effect risk in every person.
| Feature | Dihydrocodeine | Codeine |
| Medicine type | Opioid painkiller | Opioid painkiller; analgesic effect depends substantially on conversion to morphine |
| Typical UK role | Moderate to severe pain; may also be used for long-term pain when weaker painkillers have not worked | Acute moderate pain when other analgesics such as paracetamol or ibuprofen alone are not enough |
| UK availability | Prescription only | Codeine itself is prescription only; lower-strength codeine also exists in some combination pharmacy medicines |
| Approximate oral potency | Same broad FPM potency category as codeine; conversion is only an estimate | Same broad FPM potency category as dihydrocodeine; response varies, partly because of CYP2D6 metabolism |
| Formulations | Standard tablets, slow-release tablets and liquid are available | Usually tablets or oral liquid; combination products also exist |
| How quickly it works | Depends on formulation; standard tablets can take about 1.5-2 hours to work fully | Timing varies by product and patient; it should not be assumed to work identically in everyone |
| Common side effects | Constipation, nausea/vomiting, sleepiness, dizziness | Constipation, nausea/vomiting, sleepiness/tiredness; other opioid effects can occur |
| Dependence/addiction | Possible, especially with repeated or prolonged use | Possible, especially with repeated or prolonged use |
| Can they be swapped mg-for-mg? | No – opioid switching requires professional assessment | No – opioid switching requires professional assessment |
Codeine is an opioid painkiller used for pain, including acute moderate pain when medicines such as paracetamol or ibuprofen have not provided enough relief. Codeine itself is available on prescription in the UK, while lower-strength codeine can also be found in certain combination medicines with other painkillers.
Codeine is a centrally acting weak analgesic. Its analgesic effect depends on conversion to morphine, mainly through CYP2D6. Because CYP2D6 activity differs between people, some patients may get less pain relief while others may be exposed to higher morphine levels and a greater risk of opioid toxicity.
For a fuller explanation of codeine as a pain medicine, read Codeine for Pain Relief.
Dihydrocodeine is also an opioid painkiller. The NHS describes it as a medicine used for moderate to severe pain, including pain after an operation or serious injury, and for some long-term pain when weaker painkillers have not worked well enough.
It works through the opioid system to reduce pain signalling in the central nervous system and brain. Dihydrocodeine is available in different formulations, including standard and slow-release tablets, so its onset and duration depend partly on the product being used. NHS guidance notes that standard tablets can take around 1.5 to 2 hours to work fully, while slow-release tablets may take longer but last longer.
For the broader medicine overview, see What Is Dihydrocodeine: Uses, Side Effects and How It Works.
Neither medicine is automatically the better opioid for every person or every type of pain. The NHS specifically notes that dihydrocodeine is not better than other opioids for treating a particular condition, although it may be more suitable for some people depending on other health conditions and painkillers already tried.
The important point is that “stronger” does not automatically mean “better”. A medicine that is more sedating, poorly tolerated or unsuitable for a person’s health conditions is not a better option simply because it is perceived as stronger.
A switch may sometimes be considered, but codeine and dihydrocodeine should not be treated as direct mg-for-mg substitutes without professional guidance. The Faculty of Pain Medicine states that opioid switching should be recommended or supervised by a healthcare practitioner with appropriate competence and that conversion factors are only approximate.
When clinicians change one opioid to another, they consider relative potency, formulation, the reason for the change, side effects, age, frailty and the individual response. The calculated equivalent dose may also need to be reduced for safety. This is why patients should not use online conversion tables to change their own opioid dose.
Both medicines share important opioid risks. Common effects can include constipation, nausea or vomiting and sleepiness. Dizziness can also occur, particularly with dihydrocodeine. Serious opioid effects can include slow, weak or shallow breathing, especially when too much is taken or when opioids are combined with other sedating substances.
Alcohol can increase drowsiness and other side effects with opioids. Sedating medicines, including some sleeping tablets, tranquillisers, antihistamines and medicines used for mental health conditions, may also increase risk. Patients should tell their prescriber or pharmacist about other medicines and should not combine opioid painkillers unless specifically advised.
NHS guidance also warns that taking dihydrocodeine together with painkillers that contain codeine can increase side effects. This is another reason not to “top up” one opioid with the other without professional advice.
Both codeine and dihydrocodeine can cause physical dependence and addiction. Risk generally becomes more important with repeated or prolonged use, and patients who have been taking an opioid regularly should not stop it suddenly without advice because withdrawal symptoms can occur.
If you want a more detailed explanation of regular dihydrocodeine use, tolerance, dependence and stopping treatment, read Can You Take Dihydrocodeine Every Day?.
There is no universal winner. Current UK opioid-equivalence guidance places oral codeine and dihydrocodeine in a broadly similar approximate potency range, while clinical suitability depends on the individual, the type of pain, previous treatment, formulation and safety factors.
If the question is specifically about choosing or changing a prescription opioid, the decision should be made with a prescriber or pharmacist rather than by comparing milligram numbers. A higher dose number does not necessarily mean a medicine will be safer, more effective or more appropriate.
For a wider comparison with medicines such as paracetamol, ibuprofen and tramadol, see Dihydrocodeine vs Other Painkillers.
Current UK opioid-conversion guidance does not support using “twice as strong” as a simple rule. The Faculty of Pain Medicine places oral codeine phosphate and dihydrocodeine in the same approximate potency category, while stressing that conversion figures are estimates and patient response varies.
There is no reliable one-size-fits-all winner because formulation matters. For dihydrocodeine, NHS guidance says liquid may work in around 30 to 60 minutes, while standard tablets can take around 1.5 to 2 hours to work fully. Codeine timing also varies by product and individual response.
Do not combine them unless a healthcare professional has specifically told you to. NHS guidance warns that taking dihydrocodeine with painkillers containing codeine can increase side effects, and MHRA opioid-safety advice warns against using additional opioids to “top up” pain relief without professional advice.
Yes, both can cause dependence and addiction. The risk is especially important with repeated or prolonged use, so take the prescribed medicine only as directed and discuss any concerns about tolerance, dependence or stopping treatment with a healthcare professional.
Speak to the prescriber or pharmacist rather than increasing the dose or switching opioids yourself. They can review the cause of pain, how the medicine is being used, side effects, other medicines and whether a different treatment approach is appropriate.
For more educational medicine information, visit the Forever Care Meds Medicine Guides hub.
