Written by Salim Miah MPharm, Independent Prescriber · GPhC 2081653
The message tends to arrive in two parts. First the booking request: “Can I get the 25g high-dose vitamin C drip on Saturday?” Then, a few minutes later, once they have read the small print on our website: “Why do I need a G6PD test first? I’ve never heard of it. Is that just an extra charge?”
It is a fair question, and I would rather answer it properly than have anyone think we are padding the bill. I am a prescribing pharmacist, and our clinic at Listerhills Science Park in Bradford offers intravenous vitamin C alongside our other drips. The G6PD rule is one I feel strongly about. It is there because of a handful of published cases that, once you have read them, are difficult to forget.
The short answer: high-dose intravenous vitamin C is generally well tolerated by people who have been properly assessed, but it is not harmless for everyone. In people with G6PD deficiency, an inherited enzyme condition that many carriers do not know they have, very large doses have been reported to cause red blood cells to break down, sometimes with serious kidney injury. That is why we ask for a G6PD blood test before any vitamin C infusion above 8g, and why we also check kidney health, diabetes and medication history before we go ahead.
What is a high-dose vitamin C drip, and how is it different from a tablet?
Most of us need surprisingly little vitamin C. The NHS advises that adults need 40mg a day, and that you should be able to get all of it from a normal diet. An orange or a handful of peppers will do it. The same NHS page notes that taking more than 1,000mg a day as supplements can upset your stomach.
A high-dose drip is a different thing entirely. We are talking about grams, not milligrams. Our 8g infusion is roughly two hundred times the daily requirement, and the 25g infusion more than six hundred times.
The reason people choose a drip over a tablet is absorption. Your gut acts like a strict doorman. Swallow more vitamin C and it simply lets less of it through, which keeps blood levels within a narrow range. A drip skips the doorman altogether. In a 2004 pharmacokinetic study in the Annals of Internal Medicine, researchers at the US National Institutes of Health found that a 1.25g oral dose produced peak blood levels of about 135 micromoles per litre, against roughly 885 for the same dose given intravenously. Their modelling predicted that even the maximum tolerated oral dosing would plateau at around 220, while a 50g drip could reach over 13,000.
That huge jump is the whole point of intravenous vitamin C. It is also the reason it needs to be treated as a medicine rather than a smoothie. Concentrations that high behave differently in the body.
What is G6PD deficiency?
G6PD stands for glucose-6-phosphate dehydrogenase, an enzyme that protects red blood cells from oxidative damage. Think of it as the cell’s own rust protection. Without enough of it, red cells are more fragile when they come under chemical stress, and they can break apart. Doctors call this haemolysis.
It is far from rare. A systematic review published in Blood Cells, Molecules and Diseases estimated that around 400 million people worldwide are affected, making it the most common enzyme deficiency there is. Most of them are well, and most will never have a problem, as long as they avoid certain triggers.
Patient information from University College London Hospitals NHS Foundation Trust explains that it is more common in people of Mediterranean, Middle Eastern, Asian and African descent, that many people do not know they have it, and that the only way to find out is a specific blood test. Known triggers include some infections, certain medicines and fava (broad) beans.
That last point matters to me as a Bradford clinician. This is one of the most diverse cities in the country. According to Bradford Council’s analysis of the 2021 Census, around a quarter of the district’s population is of Pakistani origin, the second-highest proportion of any area in England. Many of the people who walk through our door come from backgrounds where G6PD deficiency is more common, and plenty of them will never have been tested, because nothing has ever given them a reason to be.
Why does high-dose vitamin C matter if you have G6PD deficiency?
At normal dietary levels, vitamin C works as an antioxidant. At very high concentrations in the blood, the chemistry changes. It can generate hydrogen peroxide, which is precisely the kind of oxidative stress that red cells low in G6PD struggle to cope with.
The case that stays with me was published in the Medical Journal of Australia in 2018. A man in his fifties, already being treated for prostate cancer, went to an integrative health clinic for intravenous vitamin C alongside his conventional care. He received 30g, felt unwell, and four days later was given a further 60g. He developed severe haemolysis, his haemoglobin fell to less than half its previous level, and his kidneys stopped working. He needed blood transfusions, ten days of dialysis and three weeks in hospital before his kidney function recovered.
The detail that matters most is this: the clinic’s own pre-treatment blood tests had already shown he was G6PD deficient. The result was there. It was not acted on.
Cases like this are uncommon, and the published reports have generally involved doses far higher than the ones we give. I find that reassuring, but it does not change my position. A wellness drip is something you choose, not something you need. When the downside is a hospital admission and the safeguard is a simple blood test, I would rather test.
So our rule is simple. Any vitamin C infusion above 8g, which on our menu means the 25g dose, needs a G6PD result first. If the result shows a deficiency, we will not give high-dose vitamin C, and we will explain why and what it means for you more generally, including which medicines and foods are worth knowing about.
Is high-dose vitamin C hard on the kidneys?
G6PD is the headline risk, but it is not the only one. When the body breaks vitamin C down, one of the by-products is oxalate, the same substance that forms the most common type of kidney stone. In large enough amounts, oxalate crystals can settle in the kidney itself.
This is known as oxalate nephropathy, and it has been reported after intravenous vitamin C. A case published in the American Journal of Kidney Diseases in 2013 described acute kidney injury in a patient with lupus, an autoimmune condition, who had recently been given intravenous vitamin C. Again, it is rare. Again, the people most at risk tend to share features we can ask about in advance.
Before a high-dose infusion, we want to know about:
- any history of kidney disease or reduced kidney function
- previous kidney stones, particularly calcium oxalate stones
- conditions or past surgery that affect how you absorb fat, which can raise oxalate levels
- iron overload conditions such as haemochromatosis
- pregnancy or breastfeeding
- any regular medicines, supplements or other infusions you are having
If something on that list applies, it does not automatically rule you out of every drip, but it may rule out high-dose vitamin C, and it will always prompt a proper conversation first.
Can a vitamin C drip affect blood sugar readings?
This one surprises people, and it is the safety point I raise most often with patients who have diabetes, and in Bradford I see a lot of them.
High-dose vitamin C does not raise your actual blood sugar. What it can do is fool some glucose meters. Many finger-prick meters work by an electrochemical reaction, and vitamin C at very high concentrations can trigger that same reaction, so the meter reads it as sugar. Doctors call the result pseudohyperglycaemia: a reading that looks high when your real blood glucose is normal.
A 2020 review in Critical Care set out why this matters. If someone sees a falsely high reading and gives themselves extra insulin to correct it, they could drop their real blood sugar dangerously low. Laboratory tests are not affected in the same way.
If you use insulin or another medicine that can cause hypoglycaemia, or you rely on a home meter or a continuous glucose sensor, tell us before your appointment. We will talk through how to interpret readings over the following hours and whether a high-dose infusion is sensible for you at all. Some sensor manufacturers list vitamin C as a substance that can affect readings, so it is worth checking the instructions for your own device too.
Does high-dose vitamin C actually do anything?
I would not be doing my job if I wrote about safety and skipped this part.
Intravenous vitamin C has been studied seriously in hospital medicine, most notably for sepsis. The largest trial, LOVIT, published in the New England Journal of Medicine in 2022, gave 872 adults in intensive care either vitamin C (50mg per kilogram every six hours for up to four days) or a placebo. It did not help. At 28 days, 44.5% of the vitamin C group had died or had persistent organ dysfunction, against 38.5% in the placebo group. The researchers concluded it should not be used for sepsis outside trials.
That was a very different setting from a wellness clinic, but it is a useful reminder that “natural” and “more” do not automatically mean “better”. There is also research into vitamin C alongside cancer treatment, but it remains an area for oncology teams and clinical trials, not for a private drip. If you are having treatment for cancer, please speak to your oncology team before considering any vitamin infusion, and tell us if you are.
The UK advertising regulator has been equally clear. The Committee of Advertising Practice’s guidance on intravenous nutritional therapy says claims about energy, mood and immunity are likely to be problematic without robust evidence, and that claims to treat or prevent illness are unlikely to be acceptable at all. That is why you will not see us promise any of those things. People choose vitamin C drips for their own sense of wellbeing, and that is a reasonable personal choice, provided it is made with clear information and a proper safety check behind it.
What happens at a vitamin C drip appointment in Bradford?
Every IV treatment at our clinic starts with a suitability assessment, and high-dose vitamin C has a few extra steps. In practice it looks like this.
We take a health and medication history, including the kidney, diabetes and iron questions above. For any vitamin C dose above 8g, we need a G6PD blood test result before the infusion is booked. Depending on your history, we may also suggest checking your kidney function first. Prescription-only treatments are prescribed by our pharmacist independent prescriber, with GP clinical governance, and every infusion is given by trained clinical staff with anaphylaxis-trained staff on site.
On the day, the infusion runs slowly, and we check how you are feeling throughout. We will ask you to drink water and keep well hydrated afterwards. If you feel unwell, notice dark or reduced urine, unusual tiredness or breathlessness, or yellowing of the skin or eyes in the days after, contact us and seek medical advice promptly.
If you are not sure a vitamin drip is right for you at all, that is a perfectly good place to start. I have written more generally about whether IV vitamin drips actually work, and about what the evidence says on IV drips. You can see our full menu, prices and suitability information on our IV therapy page, and read how we approach clinical oversight on our clinical safety and governance page.
Why we would rather say no
Every so often, a G6PD result or a kidney history means we tell someone that high-dose vitamin C is not for them. I understand that can be disappointing. You have made time, perhaps driven in from Leeds or Halifax, and you came for a particular treatment.
But I trained as a pharmacist at the University of Bradford, and the habit that sticks with you from that training is simple: every substance is a medicine at some dose. Vitamin C in an orange is food. Vitamin C at 25g in a vein is a drug, with a drug’s benefits and a drug’s risks. Treating it with that respect is not caution for its own sake. It is the whole reason a clinic like ours should exist.
If you would like to talk it through first, with no obligation, message us or call, and one of the team will be happy to help.
Frequently asked questions
Why do I need a G6PD test before a vitamin C drip?
Very high doses of intravenous vitamin C can cause red blood cells to break down in people with G6PD deficiency, an inherited condition many people do not know they have. A simple blood test identifies it, so we ask for one before any vitamin C infusion above 8g.
Is G6PD deficiency common?
Yes. An estimated 400 million people worldwide have it. It is more common in people of Asian, Middle Eastern, African and Mediterranean heritage. Most people with it are well and never have symptoms unless exposed to a trigger.
Do I need a G6PD test for the 8g vitamin C drip?
Our policy requires G6PD testing for infusions above 8g. Every drip, including the 8g dose, still starts with a suitability assessment, and we may recommend testing at lower doses depending on your history.
Can people with kidney problems have a vitamin C drip?
Vitamin C is broken down into oxalate, which is cleared by the kidneys and can form crystals. If you have kidney disease or a history of kidney stones, high-dose vitamin C is usually not appropriate. Tell us at assessment and we will advise.
Will a vitamin C drip affect my blood sugar meter?
It can. High-dose vitamin C may cause some finger-prick meters and sensors to show falsely high glucose readings for a period after the infusion. If you have diabetes, especially if you use insulin, tell us beforehand so we can plan safely.
Is a vitamin C drip a treatment for illness?
No. Intravenous vitamin C at our clinic is a wellbeing treatment, not a treatment for any medical condition. If you have symptoms that need explaining, your GP is the right first step.
Sources
- NHS: Vitamin C
- Padayatty SJ et al. Vitamin C pharmacokinetics: implications for oral and intravenous use. Ann Intern Med, 2004
- Nkhoma ET et al. The global prevalence of G6PD deficiency: a systematic review and meta-analysis. Blood Cells Mol Dis, 2009
- UCLH NHS Foundation Trust: G6PD deficiency patient information
- Bradford Council: Ethnicity and religion, 2021 Census
- Rees DC et al. Massive oxidative haemolysis and renal failure caused by high dose vitamin C. Med J Aust, 2018
- Cossey LN et al. Oxalate nephropathy and intravenous vitamin C. Am J Kidney Dis, 2013
- Zhang Y, Huang W. Pseudohyperglycemia when administering high-dose intravenous vitamin C. Crit Care, 2020
- Committee of Advertising Practice: Healthcare, intravenous nutritional therapy
- Lamontagne F et al. Intravenous vitamin C in adults with sepsis in the intensive care unit (LOVIT). N Engl J Med, 2022
Salim Miah MPharm is a GPhC-registered pharmacist and independent prescriber (GPhC 2081653), and the founder of Pulse and Clarity Clinic in Bradford. He graduated from the University of Bradford in 2014 and has worked across community pharmacy, hospital and general practice, where he continues to practise as a prescribing pharmacist. His specialist interests are diabetes and women’s health.