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Limited evidenceGut health

Diamine Oxidase (DAO)

The enzyme that breaks down histamine in the gut, sold for histamine intolerance. Two small randomized trials in related conditions are cautiously positive, while histamine intolerance itself still has no completed trial.

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What the science says

  • Migraine in people with low DAO Limited evidence

    A randomized double-blind trial in episodic migraine patients selected for DAO deficiency found shorter headache duration with supplementation. It was a small trial in a preselected group and has not been replicated.

  • Chronic spontaneous urticaria Limited evidence

    A randomized, double-blind, placebo-controlled study of DAO supplementation in chronic spontaneous urticaria reported symptom improvement. The sample was very small and the effect modest.

  • Histamine intolerance itself Limited evidence

    Despite being the main marketing claim, no completed randomized trial has tested DAO for histamine intolerance. A trial protocol has been published, but results are not yet available.

Dosage & safety

Studied doseTrials used a porcine-kidney DAO preparation taken before meals up to three times daily for about a month. Commercial products state activity in histamine-degrading units, and these vary widely between brands.
SafetyWell tolerated in the short trials. It is derived from porcine kidney, so unsuitable for pork-free diets, and it acts only in the gut, doing nothing about histamine already absorbed. Symptoms attributed to histamine intolerance overlap with mast cell disorders, allergy and IBS, which need proper assessment.

How to take it

TimingTake it 15 to 30 minutes before a meal likely to contain histamine.
With food?Just before food rather than with it, so it is already in the gut when the meal arrives.
Worth knowingIt only breaks down histamine in food, so it does nothing for a reaction already underway.

Frequently asked questions

Does DAO work for histamine intolerance?

No completed randomized trial has tested diamine oxidase for histamine intolerance itself, so the evidence is limited. Small trials in migraine with DAO deficiency and in chronic urticaria are cautiously positive.

When should I take DAO enzyme?

Take diamine oxidase 15 to 30 minutes before a meal likely to contain histamine, so it is in the gut when the food arrives. DAO does nothing for a reaction already underway.

Does DAO help migraines?

One small randomized double-blind trial in episodic migraine patients with DAO deficiency found shorter headache duration with diamine oxidase, but it has not been replicated, so the evidence is limited.

Is diamine oxidase safe?

Diamine oxidase was well tolerated in short trials. It is derived from porcine kidney, so it is unsuitable for pork-free diets, and symptoms blamed on histamine intolerance overlap with mast cell disorders, allergy and IBS that need assessment.

Scientific references

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