G6PD deficiency medication allergies are a critical safety concern for the estimated 400 million people worldwide living with this inherited enzyme disorder. In the UK, G6PD deficiency is most prevalent among individuals of African, South Asian, Middle Eastern, and Mediterranean descent. Unlike true immunological drug allergies, reactions in G6PD deficiency are pharmacological — certain medicines trigger oxidative stress that destroys red blood cells, causing potentially serious haemolytic anaemia. Understanding which medications to avoid, how to recognise a reaction, and how to prescribe safely is essential for both patients and clinicians.
Summary: G6PD deficiency causes red blood cells to break down when exposed to certain medications, foods, and chemicals, making careful drug selection essential to prevent potentially serious haemolytic anaemia.
- G6PD deficiency is an X-linked inherited enzyme disorder that leaves red blood cells vulnerable to oxidative damage from specific drugs, foods, and chemicals.
- High-risk medications include primaquine, tafenoquine, rasburicase, methylene blue, nitrofurantoin, dapsone, and sulfonamides — several are contraindicated per their MHRA-approved SmPCs.
- Reactions are pharmacological and metabolic, not true immunological allergies, but require the same level of drug avoidance and clinical vigilance.
- G6PD testing is mandatory before prescribing primaquine or tafenoquine, and testing during an acute haemolytic episode may give a falsely normal result.
- Symptoms of a haemolytic episode — including dark urine, jaundice, and sudden fatigue — require urgent medical review; severe symptoms warrant a 999 call or immediate A&E attendance.
- Safe prescribing relies on BNF monograph checks, MHRA SmPC review, prominent recording of G6PD status in medical records, and pharmacist involvement at the point of dispensing.
Table of Contents
- What Is G6PD Deficiency and Why It Affects Medication Safety
- Medications Known to Trigger Reactions in G6PD Deficiency
- Recognising an Adverse Drug Reaction With G6PD Deficiency
- Safe Prescribing for People With G6PD Deficiency in the UK
- How to Manage Medication Risks and Avoid Harmful Triggers
- Frequently Asked Questions
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What Is G6PD Deficiency and Why It Affects Medication Safety
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common inherited enzyme disorder worldwide, affecting an estimated 400 million people globally. In the UK, it is more prevalent among individuals of African, South Asian, Middle Eastern, and Mediterranean descent. The condition is X-linked, meaning it predominantly affects males. Females can also be affected: those who carry two copies of the defective gene are typically deficient, and even female carriers (heterozygotes) may experience variable symptoms due to X-inactivation (lyonisation), which can result in a mixed population of red blood cells with unpredictable enzyme activity.
G6PD is a critical enzyme found in red blood cells. Its primary role is to protect red blood cells from oxidative damage by producing a molecule called NADPH, which in turn maintains glutathione in its active, protective form. When G6PD activity is reduced or absent, red blood cells become highly vulnerable to oxidative stress. Under normal circumstances, this may cause no symptoms at all — many people live their entire lives unaware of the condition.
The danger arises when the body is exposed to oxidative triggers, including certain medications, infections, foods such as fava beans (broad beans), and chemical agents such as naphthalene (found in some mothballs). These triggers overwhelm the red blood cells' limited defences, causing them to break down prematurely — a process known as haemolysis. This can lead to haemolytic anaemia, a potentially serious condition. Understanding this mechanism is essential for medication safety, as some commonly prescribed drugs can inadvertently provoke a haemolytic episode in individuals with G6PD deficiency. Awareness among both patients and prescribers is therefore a key component of safe clinical care.
Medications Known to Trigger Reactions in G6PD Deficiency
A range of medications are known to carry oxidative risk in people with G6PD deficiency. The British National Formulary (BNF) includes G6PD-specific warnings within individual drug monographs, and MHRA-approved Summary of Product Characteristics (SmPCs) for individual medicines set out contraindications and cautions. The degree of risk can vary depending on the severity of an individual's G6PD deficiency and the specific genetic variant involved.
Medications contraindicated or carrying high haemolytic risk include:
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Antimalarials — primaquine and tafenoquine carry the highest risk and are contraindicated in patients with significant G6PD deficiency; G6PD testing is required before either drug is prescribed, as specified in their SmPCs and UKHSA malaria prevention guidelines. Chloroquine is generally considered safe at standard doses, but prescribers should check the BNF and relevant SmPC and seek specialist advice if uncertain.
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Antibiotics and sulfones — nitrofurantoin (used for urinary tract infections) and co-trimoxazole (trimethoprim–sulfamethoxazole) should be used with caution or avoided; dapsone (a sulfone used in dermatology, leprosy, and Pneumocystis pneumonia prophylaxis) carries a high risk of haemolysis and should be avoided where possible
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Sulfonamides — as a class, these carry haemolytic risk in G6PD deficiency; check the BNF and SmPC for individual agents
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Rasburicase (used in tumour lysis syndrome) — contraindicated in G6PD deficiency per its SmPC (Fasturtec)
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Methylene blue (Proveblue, used in methaemoglobinaemia) — contraindicated in G6PD deficiency; it is both ineffective and potentially harmful, as its mechanism of action depends on G6PD-generated NADPH. Methaemoglobinaemia in a G6PD-deficient patient requires urgent specialist input; high-dose ascorbic acid or exchange transfusion may be considered under specialist guidance.
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High-dose aspirin — some evidence associates doses above analgesic range with haemolytic risk in G6PD deficiency, though evidence is variable; standard low-dose aspirin (75 mg) is generally considered acceptable. Prescribers should check the BNF and SmPC for the specific product.
It is equally important to recognise that many medications are safe to use in G6PD deficiency, including paracetamol, most penicillins, and standard-dose ibuprofen. Patients should not avoid all medications out of caution, as this can lead to undertreated conditions. Instead, any new prescription should be reviewed in the context of the individual's G6PD status, ideally with input from a pharmacist or GP. For medicine-specific risk, always consult the current BNF monograph and the MHRA/EMC SmPC for the relevant product.
Recognising an Adverse Drug Reaction With G6PD Deficiency
When a person with G6PD deficiency is exposed to an oxidative trigger such as a high-risk medication, haemolysis can begin within hours to a few days. Recognising the signs early is critical, as severe haemolytic anaemia can become a medical emergency if left untreated.
Common symptoms of a haemolytic episode include:
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Sudden onset of fatigue and weakness — often the earliest sign
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Pallor or yellowing of the skin and eyes (jaundice) — caused by the release of bilirubin from broken-down red blood cells
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Dark or tea-coloured urine — a hallmark sign indicating haemoglobin is being excreted through the kidneys
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Shortness of breath and rapid heart rate
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Abdominal or back pain
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Dizziness or light-headedness
These symptoms can be mistaken for other conditions, including viral illness or a urinary tract infection — particularly problematic given that some UTI treatments (such as nitrofurantoin) are themselves triggers. If a patient with known G6PD deficiency develops any of the above symptoms shortly after starting a new medication, this should be treated as a potential adverse drug reaction until proven otherwise.
When to seek urgent help:
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Call 999 or go to A&E immediately if you or someone else experiences severe breathlessness, chest pain, collapse, confusion or difficulty staying awake, very dark urine with reduced urine output, or rapidly worsening jaundice.
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Contact NHS 111 or your GP urgently for other concerning symptoms such as new jaundice, significant fatigue, or dark urine after starting a new medicine.
Healthcare professionals should be aware that laboratory findings during a haemolytic episode typically include a drop in haemoglobin, raised bilirubin, elevated lactate dehydrogenase (LDH), raised reticulocyte count, reduced or absent haptoglobin, and the presence of Heinz bodies and bite cells on a blood film. The direct antiglobulin test (DAT) is typically negative, distinguishing this from immune-mediated haemolysis. Prompt recognition and withdrawal of the offending drug are the most important initial steps in management. The culprit medicine and related high-risk agents should be permanently avoided or reviewed by a specialist before any future use.
Safe Prescribing for People With G6PD Deficiency in the UK
Good practice in the NHS is to record G6PD deficiency prominently in a patient's medical records and to enable prescribing alerts within clinical systems, so that clinicians are notified before potentially harmful medications are issued. The BNF includes specific G6PD warnings within individual drug monographs, and prescribers should consult these — alongside the MHRA-approved SmPC for each medicine — before initiating treatment in at-risk individuals.
For patients who have not yet been tested but belong to a higher-risk ethnic group, or who have a family history of the condition, G6PD screening may be appropriate before prescribing certain medications. In particular:
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Primaquine and tafenoquine for malaria prevention or treatment require G6PD testing before use, as mandated by their SmPCs. UK guidance on antimalarial prescribing — including G6PD testing requirements — is provided by the UKHSA ('Guidelines for malaria prevention in travellers from the UK') and TravelHealthPro (NaTHNaC).
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Rasburicase is contraindicated in G6PD deficiency; G6PD deficiency should be excluded before use per its SmPC.
Testing involves a blood test measuring G6PD enzyme activity. It is important to note that testing during or shortly after an acute haemolytic episode may give a falsely normal result, as older G6PD-deficient red blood cells will have been destroyed, leaving a younger population with relatively higher enzyme activity. The assay should ideally be repeated once the patient has recovered.
Pharmacists play a vital role in this process. Community pharmacists are well-placed to identify potential risks when dispensing new prescriptions and should, as best practice, ask patients about known enzyme deficiencies — particularly when dispensing antimalarials, nitrofurantoin, or other high-risk agents.
Any suspected adverse drug reaction, including a haemolytic episode in a G6PD-deficient patient, should be reported via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk to support ongoing pharmacovigilance.
How to Manage Medication Risks and Avoid Harmful Triggers
Managing medication safety in G6PD deficiency requires a proactive, informed approach from both patients and healthcare professionals. The term 'medication allergy' is sometimes used loosely in this context, but it is important to clarify that reactions in G6PD deficiency are pharmacological and metabolic in nature — not true immunological allergies. However, the practical outcome — avoidance of specific drugs — is similar, and the same level of vigilance is required.
Key steps for patients and carers include:
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Carry a written record of your G6PD deficiency diagnosis and share it with every healthcare professional involved in your care, including dentists and pharmacists
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Consider wearing a medical alert identification (such as a MedicAlert bracelet) noting your G6PD deficiency, so that emergency clinicians are aware
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Always inform prescribers before starting any new medication, including over-the-counter products and herbal remedies
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Avoid fava beans (broad beans), naphthalene-containing products (such as some mothballs), and certain herbal preparations such as henna, which are known non-drug oxidative triggers
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Do not self-medicate with antimalarials or antibiotics without professional guidance
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Contact your GP or call NHS 111 promptly if you develop dark urine, jaundice, or sudden fatigue after starting a new medicine; call 999 or go to A&E immediately if symptoms are severe (see above)
For healthcare professionals, safe prescribing involves selecting alternative agents wherever possible. For urinary tract infections, if nitrofurantoin is unsuitable due to G6PD deficiency, alternatives such as trimethoprim alone, pivmecillinam, or fosfomycin may be considered, guided by local susceptibility data and NICE Clinical Knowledge Summary (CKS) guidance on UTIs in adults. If a high-risk drug is clinically necessary and no alternative exists, a baseline full blood count (FBC) should be obtained and repeated within 48–72 hours of starting treatment; patients should be counselled to stop the medicine and seek urgent review if symptoms of haemolysis develop.
In summary, G6PD deficiency drug-induced haemolytic reactions are preventable with the right knowledge and systems in place. Patient education, clear documentation, medical alert identification, and vigilant prescribing — guided by the BNF, MHRA/EMC SmPCs, and UKHSA guidance — are the cornerstones of safe management.
Frequently Asked Questions
Is a G6PD deficiency drug reaction the same as a medication allergy?
A G6PD deficiency drug reaction is not a true immunological allergy — it is a pharmacological and metabolic reaction in which certain medicines cause oxidative damage that destroys red blood cells. However, the practical outcome is the same: specific drugs must be avoided with the same level of vigilance as a documented allergy. Patients should inform all healthcare professionals, including dentists and pharmacists, of their G6PD deficiency before any new medicine is prescribed or dispensed.
Which common over-the-counter medicines are safe to take with G6PD deficiency?
Paracetamol and standard-dose ibuprofen are generally considered safe for people with G6PD deficiency and are widely used without issue. Low-dose aspirin (75 mg) is also generally regarded as acceptable, though high-dose aspirin carries variable haemolytic risk. Always check with a pharmacist before purchasing any over-the-counter product, including herbal remedies, as some preparations may contain oxidative agents.
Do I need a G6PD test before taking antimalarial tablets?
Yes — G6PD testing is mandatory before prescribing primaquine or tafenoquine, as both antimalarials carry a high risk of triggering severe haemolysis in G6PD-deficient individuals and their MHRA-approved SmPCs require testing prior to use. UK guidance from UKHSA and TravelHealthPro also specifies this requirement for malaria prevention in travellers. If you are unsure of your G6PD status and are planning travel to a malaria-endemic region, speak to your GP or a travel health clinic well in advance.
What is the difference between G6PD deficiency and a sulfa drug allergy?
A sulfa drug allergy is an immune-mediated hypersensitivity reaction, whereas G6PD deficiency causes a pharmacological, oxidative reaction that can be triggered by sulfonamides and related agents such as dapsone and co-trimoxazole. Both conditions require avoidance of certain sulfa-containing medicines, but the underlying mechanisms and clinical presentations differ. In G6PD deficiency, the primary concern with these drugs is haemolytic anaemia rather than the rash, fever, or anaphylaxis associated with a true sulfa allergy.
How do I get tested for G6PD deficiency in the UK?
G6PD deficiency is diagnosed with a blood test that measures G6PD enzyme activity, which your GP can arrange on the NHS. Testing is particularly recommended if you belong to a higher-risk ethnic group (African, South Asian, Middle Eastern, or Mediterranean descent), have a family history of the condition, or are about to be prescribed a high-risk medication such as primaquine. It is important to note that testing during or shortly after a haemolytic episode may give a falsely normal result, so the test should ideally be repeated once you have fully recovered.
What should I do if I accidentally take a medication that triggers G6PD deficiency symptoms?
Stop taking the medicine immediately and seek medical advice — contact your GP or call NHS 111 if you develop dark or tea-coloured urine, jaundice, or sudden fatigue after starting a new drug. Call 999 or go to A&E immediately if you experience severe breathlessness, chest pain, collapse, confusion, or rapidly worsening jaundice. Once the episode has resolved, the offending medicine and any closely related agents should be permanently recorded as high-risk in your medical notes to prevent future exposure.
The health-related content published on this site is based on credible scientific sources and is periodically reviewed to ensure accuracy and relevance. Although we aim to reflect the most current medical knowledge, the material is meant for general education and awareness only.
The information on this site is not a substitute for professional medical advice. For any health concerns, please speak with a qualified medical professional. By using this information, you acknowledge responsibility for any decisions made and understand we are not liable for any consequences that may result.
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