Opioid-Induced Constipation: Why It Happens and What Actually Helps
Why codeine, co-codamol, tramadol and stronger painkillers constipate so reliably, why it does not wear off, why the usual first-choice laxative is the wrong one here, and what to do when standard laxatives are not enough.
Part of the Constipation Guides.
Key fact: Opioid constipation does not wear off with time the way drowsiness and nausea do. It lasts as long as the opioid does, which is why a laxative is best started at the same time rather than after the problem has set in. And the usual first-line laxative for ordinary constipation — a bulk-forming fibre such as ispaghula — is not recommended here. An osmotic laxative with a stimulant laxative is used instead.
Not Sure Which Laxative to Use?
Laxatives work in four different ways, and with opioid painkillers the choice matters more than usual. Our laxatives guide compares each type, how quickly it works and who it suits, written by our GP-led clinical team.
Compare laxatives →Why opioids constipate
Opioids relieve pain by acting on opioid receptors in the brain and spinal cord. The gut wall is also densely supplied with the same receptors, and the opioid acts on those at the same time. The effects in the bowel are unhelpfully consistent, and they add up to three separate problems:
| What the opioid does in the gut | What you notice |
|---|---|
| Weakens the coordinated muscle waves that move contents along | Long gaps between bowel movements, bloating and fullness |
| Increases how much water is drawn back out of the stool, because it sits in the colon for longer | Hard, dry, pellet-like stools |
| Tightens the anal sphincter and dulls the sensation of needing to go | Straining, and a feeling of not having emptied fully |
Harder stool, moving more slowly, that is harder to pass once it arrives: this is why a single softening laxative is often not enough, and why the treatment approach differs from ordinary constipation. The same effects on the upper gut can add nausea, reflux and bloating, and the whole picture is sometimes called opioid-induced bowel dysfunction.
Which painkillers count
All opioids constipate, including the ones people do not think of as opioids:
| Often overlooked | More obvious |
|---|---|
| Codeine, including co-codamol and other combination painkillers bought over the counter | Morphine and oxycodone |
| Dihydrocodeine and co-dydramol | Fentanyl patches |
| Tramadol | Buprenorphine patches and tablets |
| Codeine-containing cough medicines | Methadone |
Co-codamol catches people out most often, because it is bought as a paracetamol product with something added. The codeine in it constipates exactly as codeine on its own does. Over-the-counter codeine products are licensed for short-term use only, for no more than three days, partly because of the risk of dependence; if you find you need them for longer, that is a reason to speak to a pharmacist or GP about the pain, not just the constipation.
3 days
Maximum use for over-the-counter codeine painkillers without advice
2
Laxatives usually used together: an osmotic and a stimulant
3 a week
Soft, formed stools without straining: the usual treatment target
Why it does not settle down
Most opioid side effects fade as the body adapts. Drowsiness and nausea usually improve within days of starting or increasing a dose. Constipation is different: the bowel develops little or no tolerance to the opioid’s effect, so the constipation continues for as long as the opioid is taken, at much the same intensity.
The practical consequence is that waiting it out does not work. If an opioid is going to be taken regularly for more than a few days, a laxative belongs in the plan from the start. It is entirely reasonable to ask for one at the point the painkiller is prescribed, rather than coming back a week later with an established problem. Keeping a bowel moving is considerably easier than clearing one that has become loaded.
Why not a bulk-forming laxative
Bulk-forming laxatives such as ispaghula husk (Fybogel) are not recommended for opioid-induced constipation. They work by increasing the volume of the stool and relying on the bowel’s normal muscle activity to move it along. Opioids specifically weaken that activity, so the result is a larger mass in a bowel less able to shift it — which can make symptoms worse and, at the extreme, contribute to a blockage.
This is the single most useful thing on this page, because extra fibre and ispaghula are the default advice for ordinary constipation, and they are often suggested by well-meaning friends, family or websites to someone taking codeine. The same caution applies to adding large amounts of bran. Fluids and gentle activity, by contrast, still help.
What is used instead
The standard approach is two laxatives that work in different ways, taken together. Each answers one part of what the opioid is doing.
| Component | What it does | Examples and timing |
|---|---|---|
| An osmotic laxative | Holds water in the stool, countering the extra absorption and keeping it soft | Macrogol (Laxido, Movicol), usually working within one to three days; lactulose, which can take up to two days and often causes wind |
| A stimulant laxative | Prompts the bowel muscle activity that the opioid is suppressing | Senna or bisacodyl tablets, usually taken at night and working in around 8 to 12 hours |
Both halves matter. Softening alone tends to leave soft stool that still does not move; stimulating alone pushes against stool that is still hard. Doses are adjusted against how the stool looks and feels — the aim is a soft, formed stool passed without straining — rather than against a set number of trips to the toilet.
Macrogol is the osmotic laxative most often chosen, and its dosing is where most problems arise: each sachet needs its full measure of water to work. That is covered in Laxido and Movicol: how to use them. Docusate, which softens the stool and has a mild stimulant effect, is a reasonable addition or alternative where straining particularly needs to be avoided. Each laxative class is compared in laxatives compared.
Alongside the laxatives, drink enough to keep your urine pale, keep as active as the underlying problem allows, and do not ignore the urge to go — the opioid has already dulled that signal, so it is worth acting on when it comes.
Short courses: dental work, injuries and surgery
Many people meet opioid constipation for the first time after a short course — co-codamol after a tooth extraction, dihydrocodeine after an injury, or stronger painkillers sent home after an operation. A few practical points apply:
- for a course of only a day or two, a laxative is often not needed, but keep fluids up and watch for the first signs
- for anything longer, or after surgery where you are also less mobile, eating less and possibly dehydrated, starting a laxative alongside the painkiller is sensible
- after abdominal, pelvic or anal surgery, or a hernia repair, avoiding straining matters more than usual; follow the advice on your discharge letter, and ask the ward pharmacist if no laxative was supplied
- when the painkiller stops, reduce and stop the laxative over a few days rather than continuing it out of habit
Older adults are at particular risk, because they are more likely to be on other constipating medicines as well — iron tablets, some antidepressants and bladder medicines, calcium supplements and some blood pressure tablets all add to the effect.
If standard laxatives are not enough
If constipation persists despite an osmotic and a stimulant laxative taken regularly, there is a clear sequence of next steps:
| Step | What it involves |
|---|---|
| Increase the doses | Under-dosing is more common than true treatment failure. Doses can usually be increased within the licensed range before anything new is added |
| Check for a blockage | Leakage of loose stool, a feeling of being blocked, or a long gap with abdominal discomfort can mean impaction. See faecal impaction and overflow |
| Suppositories or a mini enema | Useful where stool reaches the rectum but will not pass, a common pattern because of the opioid’s effect on the sphincter. Glycerol suppositories often work within 15 to 30 minutes |
| A peripherally acting opioid antagonist | Naloxegol or naldemedine tablets block the opioid’s effect in the gut without crossing into the brain, so pain relief is preserved. Prescription-only, and NICE recommends them where laxatives have not worked adequately |
| Methylnaltrexone injection | A related medicine given under the skin, used mainly where tablets are not suitable, including in palliative care |
| A change in the opioid itself | A combination tablet of prolonged-release oxycodone with naloxone is designed to reduce constipation, and some people find patches less constipating than tablets. This is a decision for the prescriber |
In palliative care
People taking opioids for cancer pain or at the end of life often need higher laxative doses than anyone else, and constipation can cause real distress, nausea and loss of appetite. Laxatives are prescribed routinely alongside the opioid in this setting, and the doses are expected to be adjusted frequently. If you are caring for someone in this situation, raise constipation with the palliative care team early; it is one of the most treatable sources of discomfort.
When to reduce the laxative
The endpoint is not simply “the opioid has stopped”. Laxatives are reduced once you are passing soft, formed stools without straining at least three times a week. If the opioid is continuing at the same dose, that usually means the laxative continues too, at the dose that keeps you there.
If the opioid dose comes down or stops, bring the laxative down with it, gradually over several days, otherwise the result swings the other way into loose stools. If the opioid dose goes up, expect to need more laxative as well.
The bigger question about the painkiller
Constipation is one of the good reasons to review whether an opioid is still earning its place. For long-term pain that is not caused by cancer, opioids are considerably less effective than was once assumed, and their side effects — constipation among the most persistent — accumulate over months and years.
Do not stop a regular opioid suddenly. After more than a few weeks of regular use, stopping abruptly can cause withdrawal symptoms, including diarrhoea, sweating, restlessness and a temporary increase in pain. Any reduction should be planned and gradual, with whoever prescribes it. But if the painkiller is not achieving much and the constipation is a daily burden, say so at your next review.
When to get help urgently
Seek urgent medical help if you have not opened your bowels for several days and have abdominal pain or swelling with vomiting and cannot pass wind — this can suggest a bowel obstruction. Also seek prompt advice for leakage of loose stool alongside a blocked feeling, which can be impaction with overflow; taking an anti-diarrhoea medicine for it would make it worse.
Speak to a GP soon, rather than adjusting laxatives yourself, if you notice blood in your stool or black stools, unexplained weight loss, or a change in bowel habit that began before the opioid or has continued for six weeks or more, particularly if you are over 50. Those need assessment in their own right, whatever painkiller you are taking.
Questions About Your Painkillers or Laxatives?
Our GPhC-registered pharmacy team can advise on constipation caused by medicines, how laxatives fit alongside your other treatment, and when you should see your GP. Contact details and opening hours are in our Help Centre.
Contact our pharmacy team →Frequently Asked Questions
Why does codeine cause constipation?
Codeine and other opioids act on receptors in the gut wall as well as the brain. They weaken the muscle waves that move stool along, increase how much water is absorbed from it, and tighten the anal sphincter while dulling the urge to go. The result is harder stool that moves more slowly and is harder to pass.
Does opioid constipation get better over time?
No. Unlike drowsiness and nausea, which usually fade within days, the bowel develops little or no tolerance to the constipating effect. It continues for as long as the opioid is taken, which is why a laxative is best started at the same time rather than later.
Which laxative is best for opioid-induced constipation?
Usually an osmotic laxative and a stimulant laxative together, such as macrogol or lactulose with senna or bisacodyl. The osmotic keeps the stool soft and the stimulant prompts the bowel activity the opioid suppresses. Bulk-forming laxatives such as ispaghula are not recommended.
Can I take Fybogel with co-codamol?
It is not recommended. Fybogel is a bulk-forming laxative, and it adds volume to stool in a bowel whose movement has been slowed by the codeine in co-codamol. That can make constipation worse and contribute to a blockage. An osmotic laxative with a stimulant laxative is used instead.
What can I take if laxatives are not working with my painkillers?
First, check that both an osmotic and a stimulant laxative are being taken regularly at an adequate dose, and that there is no blockage. If constipation persists, a prescriber can consider a peripherally acting opioid antagonist such as naloxegol or naldemedine, which blocks the opioid effect in the gut without reducing pain relief, or a change to the painkiller itself.
When can I stop the laxative?
Laxatives are reduced once you are passing soft, formed stools without straining at least three times a week. If the opioid is continuing, the laxative usually needs to continue too. When the opioid is reduced or stopped, reduce the laxative gradually over several days alongside it.
References
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Constipation. cks.nice.org.uk
- National Institute for Health and Care Excellence. Naloxegol for treating opioid-induced constipation (TA345). nice.org.uk
- National Institute for Health and Care Excellence. Naldemedine for treating opioid-induced constipation (TA651). nice.org.uk
- Medicines and Healthcare products Regulatory Agency. Codeine and dihydrocodeine-containing medicines: over-the-counter use limited to short-term treatment, with warnings about addiction. gov.uk
- NHS. Constipation. nhs.uk
- Joint Formulary Committee. British National Formulary: constipation and laxatives. bnf.nice.org.uk
- electronic Medicines Compendium. Movicol 13.7g powder for oral solution: Summary of Product Characteristics. medicines.org.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Do not stop or change a prescribed painkiller without speaking to the prescriber. A persistent change in bowel habit, rectal bleeding or unexplained weight loss should always be assessed rather than treated as constipation. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.