DAO supplements are attracting interest as a way to manage reactions to high histamine foods. Here is what to weigh up before considering one, and what the research does and does not support.
If you have been researching histamine intolerance, you have probably come across DAO supplements already. This is not a recommendation either way. It is a look at who tends to explore DAO supplementation, what is worth knowing before you do, and where the evidence currently stands.
Diamine oxidase (DAO) is an enzyme your body produces naturally to break down histamine arriving from food, in the gut, before it is absorbed.1 Supplementing it is one option some people explore alongside, not instead of, paying attention to diet.
If you are new to DAO and want to start with the basics you can read What Is DAO Enzyme? for a detailed explanation of how the enzyme works.
Who Might Consider Taking a DAO Supplement?
- You regularly notice symptoms such as headaches, flushing, digestive discomfort or hives after meals featuring aged cheese, cured meats, wine or fermented foods
- You have already reduced high histamine foods and found it helped, but find a genuinely low histamine diet difficult to sustain long term
- You want to understand the research linking DAO to migraine, chronic urticaria or histamine intolerance symptom scores before deciding whether it is relevant to you
It is important to note these are things worth raising with a GP, dietitian or qualified practitioner, rather than a checklist for self diagnosis.
When a Low Histamine Diet Might Be Enough on Its Own
If you have not yet looked at where dietary histamine is actually coming from, that is worth doing first. Histamine rises with fermentation, curing and ageing.
Mature cheese, cured meats, tinned and aged fish, wine, vinegar, fermented soy and slow ripened tomatoes all tend to run higher, and storage matters as much as the food itself, since fish accumulates histamine quickly once it is out of the cold chain. For some people, understanding and adjusting for this is enough on its own.
Supplementing an enzyme is not a substitute for that groundwork, and nothing in the current research suggests it works well in isolation from it.
Porcine or Plant DAO: Does the Source Matter?
Yes, and it is worth understanding before you choose one. DAO supplements come from two source materials. Porcine kidney protein extract is the form behind the published human trials.
The research on histamine intolerance symptom scores and the smaller studies in migraine and chronic urticaria all used this source.2, 3, 4 Plant derived DAO, typically from sprouted mung bean or pea, is vegan suitable and appealing for that reason, but it has not been studied nearly as extensively. Open questions remain about how specific it is to histamine versus other diamines, and how stable its activity stays once it is formulated into a supplement.5
If you have a reason to avoid animal derived ingredients, that is a legitimate factor in your decision. Just go in aware that the evidence base is thinner for the plant derived version.
Why Timing Before Meals Matters So Much
DAO is a protein, and stomach acid breaks down proteins. That makes delivery format central rather than a minor detail. A DAO supplement that does not survive to the small intestine intact is not going to do much.
Timing follows the same logic. Across the clinical trials, DAO was taken shortly before a meal, roughly fifteen to twenty minutes beforehand, so the enzyme is already in place as food, and the histamine in it, arrives.3, 4
Not with food, and not afterwards. If you are looking at a product, this detail is worth checking against the label.
Who Should Be More Cautious About DAO Supplements?
Speak to a GP, dietitian or qualified practitioner before starting a DAO supplement if you are pregnant or breastfeeding, taking medication, particularly anything affecting the gut or immune system, managing a diagnosed digestive or allergic condition, or genuinely unsure whether your symptoms are related to dietary histamine at all.
DAO deficiency does not have a single, reliable diagnostic test. Research using a large population sample found that DAO activity measured in blood did not consistently separate people with symptoms from those without.6 Working through what is actually going on with a professional is more useful than guessing.
If you would like to talk it through, you can book a free 15 minute consultation with a Napiers herbalist. They can look at your diet and symptoms with you and help you decide whether DAO is worth exploring, alongside advice from your GP or pharmacist.
What DAO Supplementation Is, and Is Not
It is worth being direct. DAO is not a treatment for migraine, chronic urticaria or any other named condition, and no supplement should be presented as one.
What the research shows is that in small, specific trials, DAO supplementation before meals was associated with improvements in particular measured outcomes, such as headache duration in migraine patients with confirmed DAO deficiency, and activity scores in chronic spontaneous urticaria.3, 4 That is meaningfully different from DAO being an established treatment, and the researchers behind these studies are consistently candid about the need for larger, longer trials.
Questions to Ask Yourself Before Deciding
A few honest questions help more than a rigid checklist. Have you looked at dietary histamine and food storage first? Are you working with a practitioner who can help interpret your symptoms?
Are you choosing a supplement with clear information about source and dosing timing? Are you prepared for a gradual, individual process rather than a fast or complete fix?
There is no universal answer to whether you should take DAO. It is a genuinely researched, still young option that some people explore alongside dietary changes, not a substitute for understanding your own triggers, and not a guaranteed outcome for anyone.
If you would like to look at the clinical trials in more detail, including emerging research on histamine and menopause, read DAO Enzyme, Histamine Intolerance and Menopause: What the Research Shows.
Frequently Asked Questions
How long before I would notice anything?
In the trials that showed improvements, participants took DAO for several weeks before assessment. It is not designed to work like a fast acting remedy, and individual response varies.2
Can I take DAO alongside a low histamine diet?
Yes, that is how it is used in the research. A large ongoing trial is specifically designed to test DAO supplementation, from both porcine and plant sources, alongside and against a low histamine diet, which reflects how it is actually approached in practice, as one part of a broader picture rather than a replacement for dietary awareness.7
Is DAO supplementation safe?
Early dose ranging safety research in healthy volunteers has been conducted, but the overall evidence base remains limited, particularly for those who are pregnant, breastfeeding or on regular medication. That is exactly why professional guidance matters more here than with many supplements.
Will a DAO supplement fix histamine intolerance?
No supplement should be presented as a fix for a named condition, and DAO is no exception. What has been studied is symptom improvement in small trials, not a cure, and not something that removes the need to understand your own dietary triggers.
When should I take a DAO supplement?
In the clinical trials, DAO was taken shortly before meals, so the enzyme was already in the gut as food arrived.3, 4 Follow the timing on the product label, and check with a practitioner if you are unsure.
Is plant DAO as effective as porcine DAO?
We do not know yet. The published human trials used DAO from pig kidney, while plant DAO from pea or mung bean sprouts has mostly been studied in the laboratory.5 It may suit people who prefer a vegan option, but the evidence behind it is much thinner.
Can I take DAO if I am pregnant or breastfeeding?
Speak to your GP, midwife or pharmacist before taking any supplement during pregnancy or while breastfeeding. There is very little research on DAO supplements in these groups, so professional advice should come first.
References
- Comas-Basté, O. et al. (2020). Histamine Intolerance: The Current State of the Art. Biomolecules. mdpi.com
- Schnedl, W.J. et al. (2019). Diamine oxidase supplementation improves symptoms in patients with histamine intolerance. Food Science and Biotechnology. ncbi.nlm.nih.gov
- Izquierdo-Casas, J. et al. (2019). Diamine oxidase (DAO) supplement reduces headache in episodic migraine patients with DAO deficiency: a randomised double-blind trial. Clinical Nutrition. diposit.ub.edu
- Yacoub, M.R. et al. (2018). Diamine Oxidase Supplementation in Chronic Spontaneous Urticaria: a Randomised, Double-Blind Placebo-Controlled Study. International Archives of Allergy and Immunology. karger.com
- Comas-Basté, O. et al. (2020). Lyophilised legume sprouts as a functional ingredient for diamine oxidase enzyme supplementation in histamine intolerance. LWT. sciencedirect.com
- van Odijk, J. et al. (2023). The Use of DAO as a Marker for Histamine Intolerance: Measurements and Determinants in a Large Random Population Based Survey. Nutrients. mdpi.com
- Duelo, A. et al. (2025). Study Protocol for a Prospective, Unicentric, Double-Blind, Randomised, and Placebo-Controlled Trial on the Efficacy of a Low-Histamine Diet and DAO Enzyme Supplementation in Patients with Histamine Intolerance. Nutrients. mdpi.com
