Pain
Opioid analgesics
Opioid painkillers — Strong painkillers for acute, cancer and palliative pain — effective but with dependence and overdose risks.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Opioids are powerful painkillers used for moderate to severe acute pain, pain after surgery, and cancer or palliative pain. They range from weaker agents to strong opioids such as morphine.
How it works
They act on opioid receptors in the brain and spinal cord to reduce the perception of pain. The same receptor action explains their main hazards — sedation, slowed breathing, constipation and, over time, tolerance and dependence.
In practice
In practice the priority is matching opioid use to the situation: they are valuable for acute severe pain, cancer pain and palliative care, but the evidence for long-term use in persistent non-cancer pain is weak and the risks of tolerance, dependence and harm grow with dose and duration. So we set clear goals and a review date, keep to the lowest effective dose, anticipate constipation from the outset, and counsel on the danger of combining opioids with sedatives such as benzodiazepines or gabapentinoids. Where overdose risk exists, take-home naloxone is worth discussing.
Examples
Practical use
How to take it & use it well
- Take your opioid exactly as prescribed and avoid increasing the dose yourself, as higher amounts raise the risk of harm.
- Use a regular laxative and keep well hydrated, as constipation is very common with these medicines.
- Do not drink alcohol or take other sedating medicines with them, as this can dangerously slow breathing.
- Do not drive if you feel drowsy or impaired, and be aware there are legal limits for some opioids while driving.
- Do not stop suddenly after regular use, as withdrawal symptoms can occur; reductions should be planned with your prescriber.
Common uses
- Moderate to severe acute pain
- Post-operative pain
- Cancer and palliative pain
Monitoring
- Pain relief versus side-effects, with a clear review date
- Sedation and breathing, especially when starting or increasing
- Bowel function and signs of dependence
Weighing it up
Advantages & disadvantages
Advantages
- They are effective for moderate to severe short-term pain, such as after surgery or injury.
- They are valuable for pain at the end of life and in palliative care.
- Different forms allow flexible options for both sudden and longer-lasting pain.
- When used carefully for the right pain, they can greatly improve comfort and function.
Disadvantages
- They commonly cause constipation, nausea and drowsiness.
- Regular use can lead to tolerance, dependence and addiction.
- They can slow or stop breathing in overdose, which can be fatal.
- They are often less effective for long-term non-cancer pain than people expect, with risks that can outweigh benefits.
Key safety principles
What to watch for
- Respiratory depression — the main cause of fatal overdose, greatly increased by alcohol, benzodiazepines or gabapentinoids.
- Tolerance, dependence and withdrawal; limited benefit in long-term non-cancer pain.
- Constipation is near-universal; caution in renal or hepatic impairment and in the elderly.
Key interactions
What to avoid or check alongside
- Combined with gabapentinoids, benzodiazepines, alcohol or other sedatives, they can dangerously suppress breathing.
- Taken with other medicines causing constipation, the effect adds up.
- Some medicines that change liver enzymes can raise or lower opioid levels and effects.
- Combined with certain antidepressants, some opioids can raise the risk of serotonin syndrome.
- Used with other drowsy-making medicines, the risk of falls and confusion increases, especially in older people.
Patient & carer advice
- Constipation is expected — we will usually prescribe a laxative alongside
- Never combine with alcohol or extra sedatives, and keep them locked away from others
- Do not stop a long-term opioid abruptly; report excessive drowsiness urgently
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Opioid analgesics: frequently asked questions
Why do opioids cause constipation?
They slow the movement of the bowel, so constipation is very common and often persists. A regular laxative and good fluid intake are usually recommended alongside them.
Can I drive while taking opioids?
Not if you feel drowsy or impaired. Some opioids also have legal driving limits in the UK. Do not drive until you know how the medicine affects you and you feel safe.
Are opioids addictive?
They can be. Regular use may lead to tolerance and dependence, and some people develop addiction. Using the lowest effective dose for the shortest needed time reduces this risk.
What are the signs of opioid overdose?
Very slow or shallow breathing, extreme drowsiness, pinpoint pupils and difficulty waking are warning signs. This is a medical emergency needing an urgent ambulance.
Can I stop my opioid suddenly?
After regular use, stopping suddenly can cause withdrawal symptoms. Reduce gradually with your prescriber's guidance rather than stopping all at once.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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