Mānuka Honey Side Effects: What You Should Know

Summary: Mānuka honey is a food, not a medicine, and most healthy adults and children over one year old tolerate it well. The side effects worth knowing about are narrow but important: it must never be given to babies under 12 months because of the risk of infant botulism, allergic reactions are possible although rare, and it counts as a free sugar in the same way table sugar does. A higher MGO grade indicates stronger antibacterial activity, not a stronger dose of medicine.

Is Mānuka Honey Safe?

For most people, yes. Mānuka honey is sold in the UK as a food, and for healthy adults and children over the age of one it carries the same broad safety profile as any other honey. It is not associated with the kind of adverse effects that would make it unsuitable for general use.

That said, honest answers are more useful than reassuring ones. There are four areas where Mānuka honey genuinely warrants care, and one widespread misunderstanding about what its MGO grade means. This article covers these.

Never Give Honey to a Baby Under 12 Months

This is the single most important safety point on this page, and it is not negotiable.

NHS guidance states that honey occasionally contains bacteria that can produce toxins in a baby's intestines, leading to infant botulism, which it describes as a very serious illness. The NHS advises that honey should not be given to a child until they are over one year old. 

This applies to every honey, including Mānuka, at every MGO grade. It applies to honey stirred into food or baked into a recipe, because the spores concerned are not reliably destroyed by cooking. It applies to a small taste on a spoon or a dummy just as much as it does to a full serving.

After a child's first birthday their digestive system is mature enough that the risk no longer applies in the same way. For age-appropriate guidance beyond the first year, see our parent's guide to Mānuka honey and children.

Allergic Reactions Are Rare, But They Are Real

Honey is not a single substance. It carries pollen from the plants the bees foraged, along with proteins from the bees themselves, and both can act as allergens.

Research published in the Journal of Allergy and Clinical Immunology found that allergic reactions to honey are caused both by pollen proteins carried in the honey and by proteins from the glands of honey bees. Pollen from the Compositae family, which includes plants such as ragweed and mugwort, is among the more frequently implicated sources.

How common is this? Genuinely uncommon. A 2021 review in the International Journal of Molecular Sciences noted that while the exact incidence of honey allergy is unknown, it has been estimated at less than 0.001% of the population. The same review recorded that eight allergenic protein fractions identified in bee venom have also been found in honey, which is why people with a known bee venom allergy are sometimes advised to be cautious.

Reactions that do occur range from mild itching in the mouth through to anaphylaxis. Take particular care if you have a known allergy to pollen or to bee stings, and speak to your GP or allergy specialist before trying Mānuka honey for the first time.

If you or someone else develops swelling of the lips, mouth or throat, difficulty breathing, or sudden faintness after eating honey, treat it as a medical emergency and call 999.

It Is Still a Free Sugar

This is the side effect most often left out of Mānuka honey content, and for most readers it is the one that actually applies day to day.

NHS guidance is explicit that the sugars found in honey occur naturally but still count as free sugars, in the same category as sugar added to biscuits or fizzy drinks. Free sugars are the sugars UK health guidance asks us to cut down on, and honey sits squarely among the foods the NHS names as contributing to tooth decay.

USDA composition data puts honey at roughly 82 grams of sugars per 100 grams. On that reference, a level teaspoon of around 7 grams contains close to 6 grams of sugars, which is approaching a fifth of the recommended daily free sugars allowance for an adult. Always check the label on your own jar, since that is the definitive figure for the product in your hand.

NHS recommended daily maximum for free sugars:

Two practical consequences follow. Honey contributes to tooth decay, so NHS advice on limiting free sugars to mealtimes applies to Mānuka just as it does to jam or syrup. And because it is calorie dense, it counts towards overall energy intake rather than sitting outside it. For guidance on incorporating Mānuka honey into a daily routine, see our article on getting your daily dose.

Blood Sugar and Diabetes

Mānuka honey is a carbohydrate food and it will raise blood glucose. Because UK guidance classifies honey as a free sugar, it needs to be counted in the same way as any other sugar by anyone monitoring their carbohydrate intake.

There is no good evidence that a higher MGO grade changes this. MGO relates to antibacterial activity, not to how the sugars in the honey are absorbed. A premium grade jar is not a lower sugar jar.

Mānuka honey is not a treatment for diabetes and should not be used as one. If you are living with diabetes or pre-diabetes, or you are on medication that affects blood glucose, speak to your GP or diabetes team before adding it to your diet so it can be accounted for within your own plan.

Does a Higher MGO Grade Mean More Risk?

This question comes up constantly and deserves a straight answer, including the parts that are still unresolved.

MGO stands for methylglyoxal, the naturally occurring compound responsible for the non-peroxide antibacterial activity that distinguishes Mānuka honey from other honeys. An MGO number on a jar is a measure of that compound in milligrams per kilogram. It is a marker of antibacterial potency, not a dosage instruction, and a higher number does not mean the honey is a stronger medicine.

On safety, the evidence available is limited but reassuring rather than alarming. A study published in the Journal of Agricultural and Food Chemistry in 2013 gave a defined amount of methylglyoxal in Mānuka honey to healthy volunteers and found no change in urinary excretion of methylglyoxal or D-lactate afterwards, suggesting dietary methylglyoxal is metabolised rather than accumulating. It is worth being clear that this was a very small study involving four volunteers, so it should be read as an early indication rather than a settled conclusion.

Later work has shown that methylglyoxal from Mānuka honey does react with amino compounds such as creatine and arginine during human digestion, forming glycated adducts. What that means for long-term health has not been established, and we are not going to speculate on it.

One published commentary in the literature has raised a theoretical concern that methylglyoxal, as a precursor of advanced glycation end products, might in principle delay healing when Mānuka honey is applied to diabetic foot ulcers. Two things are worth noting about it. It is a commentary rather than a clinical trial, and its authors explicitly called for randomised controlled trials to settle the question. And it concerns honey applied to a diabetic wound, not honey eaten from a jar.

The honest summary is that there is no established evidence that eating Mānuka honey in normal amounts is harmful because of its MGO content, and that the research base is thinner than the confident claims made across much of this category would suggest. If you want to understand what the grades actually mean before buying, our MGO guide covers it in full.

Eating Honey Is Not the Same as Using a Medical Honey Dressing

This is the distinction most likely to lead someone into real harm, and most likely to be blurred in marketing.

Honey used in clinical wound care is a regulated medical device, not a food. It is sterilised, typically by gamma irradiation, which removes naturally occurring microbial contamination without destroying the antibacterial activity. It is batch tested and standardised for potency, and it is manufactured under controls that food production does not require. Clinical guidance is that sterilised, laboratory-tested honey should be the product used on infected wounds.

Food-grade honey, including certified Mānuka at any MGO grade, is not sterile. It is a raw agricultural product and it can carry naturally occurring bacterial spores. Those spores are harmless when eaten by a healthy adult and are an entirely different proposition when introduced into broken skin.

Do not apply food-grade honey to open wounds, burns, surgical sites or diabetic foot ulcers. Broken skin that is not healing needs assessment by a GP, practice nurse or podiatrist, who can prescribe an appropriate dressing.

When to Speak to a Healthcare Professional

Take advice before using Mānuka honey if any of the following apply to you:

• You have a known allergy to pollen, bee stings or other bee products
• You are living with diabetes or pre-diabetes, or you monitor your blood glucose
• You are pregnant or breastfeeding and unsure how it fits your diet
• You are considering it for a wound, burn or any broken skin
• You are taking prescribed medication and are unsure how it fits with your diet
• You are caring for a child under one year old, in which case honey should be avoided entirely
  

This article is for general information and is not medical advice. It does not replace guidance from a qualified healthcare professional who knows your individual circumstances.

Why Choose Manuka Lab

Being straight about what Mānuka honey does not do is part of the same commitment as being able to prove what it is. Our honey is 100% certified New Zealand Mānuka, harvested in the remote East Cape region from the Leptospermum scoparium plant, and independently tested to New Zealand Government export standards.

Every jar carries a seven-digit batch code you can enter on our traceability page to trace the honey back through our Opotiki and Whakatane facilities to the hive it came from. If you want to know exactly what you are eating, and exactly how strong it is, the information is there rather than implied.