Morphine allergy
Reaction to morphine and related opioids.
About morphine allergy
Morphine is a strong opioid painkiller used for severe pain, related to codeine and other opioids. Many reactions attributed to it are not true immune allergy. Opioids can directly cause certain cells to release histamine, producing itching, flushing or a rash without the IgE mechanism of genuine allergy. Other common effects, such as nausea, drowsiness and constipation, are predictable pharmacological actions rather than allergy. Recognising this distinction is important, because a true allergy and a routine side effect have very different implications for future pain relief.
When reactions occur they are frequently mild: itching, a blotchy rash, hives or localised swelling from histamine release, with the onset spanning minutes to hours and some rashes appearing later. Genuine IgE-mediated morphine allergy is uncommon but can be more serious, and anaphylaxis is possible though rare. Because histamine release is partly a shared opioid characteristic, someone who reacts this way may react to related opioids too.
Management depends on separating a predictable side effect from genuine allergy, which shapes whether related opioids can be used safely. Record the reaction and tell every doctor, nurse and pharmacist. Specialist assessment can clarify the reaction and identify suitable alternative painkillers. A severe reaction with breathing difficulty, widespread swelling or collapse is a medical emergency call 999. Never take, re-take or dose the medicine without professional advice.
Common triggers
- Morphine and products containing it
Symptoms
- Skin rash, hives or itching
- Swelling of the face, lips or throat
- Wheezing or difficulty breathing
- Dizziness or a drop in blood pressure
- In severe cases, anaphylaxis
Avoidance & management
- Tell every doctor, pharmacist and dentist about the allergy
- Wear a medical-alert bracelet if advised
- Check the ingredients of combination medicines
- Discuss safe alternatives with your prescriber
- Seek emergency care for a severe reaction
Sources & references
Allergy safety: what everyone should know
Mild-to-moderate reaction signs
- Itching, hives or a raised rash
- Swelling of lips, face or eyes
- Tingling mouth, sneezing, runny nose
- Stomach pain, nausea or vomiting
Anaphylaxis — call 999 (UK) or 112 (EU) immediately
- Difficult or noisy breathing, wheeze, persistent cough
- Swelling of the tongue or tightness in the throat
- Dizziness, collapse, pale and floppy (young children)
- Use an adrenaline auto-injector (e.g. EpiPen) at once if prescribed, then call an ambulance even if symptoms improve
Allergy or intolerance? A true allergy involves the immune system and can escalate quickly; an intolerance (e.g. lactose intolerance) is unpleasant but not life-threatening. The symptoms overlap, so self-diagnosis is unreliable.
Getting tested: home-testing kits based on IgG are not diagnostically valid. If you suspect an allergy, ask a GP for referral to an allergy clinic for skin-prick or specific-IgE testing and a supervised food challenge where appropriate.