RetzlerRx® Hist Arrest provides 20,000 Histamine Degrading Units (HDU) of diamine oxidase per tablet. DAO is an enzyme concentrated in the intestinal mucosa that helps metabolize histamine contained in food before much of that histamine is absorbed. Taken before meals, supplemental DAO can provide targeted digestive support when dietary histamine is a concern.*
RetzlerRx® Hist Arrest is a targeted DAO enzyme formula designed to support the metabolism of histamine from food within the digestive tract.* Each tablet provides 20,000 Histamine Degrading Units (HDU) of diamine oxidase.
DAO has a fairly specific role. It is highly active at the intestinal barrier, where it helps break down extracellular histamine encountered through food. This makes supplemental DAO most relevant around meals, particularly when foods that are aged, fermented, cured or otherwise higher in histamine are part of the diet.*
One-Minute Read
Histamine is a normal signaling molecule involved in immune activity, digestion, blood-vessel regulation and nervous-system function. It is also present in food. Aged cheeses, cured meats, fermented foods, wine, beer and certain fish can contain considerably more histamine than freshly prepared foods.
Diamine oxidase, or DAO, is one of the enzymes the body uses to metabolize this dietary histamine. It is concentrated in the intestinal mucosa, where it helps break down histamine before it moves from the digestive tract into the circulation.
Hist Arrest supplies 20,000 HDU of DAO per tablet and is intended to be taken before meals. Its purpose is targeted rather than systemic: helping support the handling of histamine arriving through food.* DAO is not the same as an antihistamine medication, does not block histamine receptors throughout the body, and should not be used as protection against a known food allergy.
For people who notice a consistent relationship between certain foods and symptoms, DAO can be one practical tool while the broader pattern of diet, gastrointestinal health and individual tolerance is considered.
- Supporting dietary histamine breakdown before meals.*
- Supporting digestive comfort around histamine-containing foods.*
- Providing additional intestinal DAO enzyme activity.*
- Adults who notice a reproducible sensitivity to histamine-rich foods.*
- Targeted, meal-time histamine support rather than a broad systemic antihistamine approach.*
What Is DAO?
Diamine oxidase (DAO) is an enzyme involved in the metabolism of extracellular histamine. It is particularly abundant in the intestinal mucosa and is most active in the small intestine.
Within the gastrointestinal tract, DAO helps form part of the metabolic barrier between histamine contained in food and the bloodstream. Histamine that is broken down within the intestinal lumen is less available for absorption.*
This is also why oral DAO supplementation is generally used shortly before eating rather than taken randomly during the day. Its intended action occurs in relation to dietary histamine entering the digestive tract.
Histamine in Food
Histamine is formed when certain microorganisms convert the amino acid histidine into histamine. Concentrations can increase during fermentation, aging, curing and storage, which is why some foods are more commonly associated with higher histamine exposure.
Examples can include:
- Aged and matured cheeses
- Cured and processed meats
- Fermented foods
- Wine and beer
- Certain fish and seafood
- Foods stored as leftovers for extended periods
These foods are not inherently unhealthy, and not everyone needs to avoid them. Histamine content varies considerably from one food and preparation method to another, and individual tolerance varies as well.
20,000 HDU Per Tablet
DAO products are generally described according to Histamine Degrading Units, or HDU, which express enzyme activity rather than simply the physical weight of the ingredient.
Each RetzlerRx® Hist Arrest tablet provides 20,000 HDU of diamine oxidase for targeted meal-time support.*
What Hist Arrest Is Designed to Support
- Dietary Histamine Metabolism: Provides supplemental DAO activity to support the breakdown of histamine from food.*
- Digestive Comfort: May support greater comfort around meals containing histamine-rich foods.*
- Intestinal Histamine Handling: Supports the enzymatic processing of dietary histamine within the gastrointestinal tract.*
- Targeted Meal-Time Support: Designed to be used in relation to meals rather than as a general systemic histamine supplement.*
DAO Is Not an Antihistamine
DAO supplements and antihistamine medications work differently.
Antihistamine medications generally act by blocking histamine receptors, such as H1 or H2 receptors. Supplemental DAO is an enzyme. Its intended role is to help metabolize histamine while that histamine is still within the digestive tract.*
That distinction is clinically useful because many symptoms commonly attributed to “histamine” do not necessarily result from dietary histamine exposure. Headaches, flushing, itching, abdominal symptoms and nasal symptoms can have many causes.
Histamine Intolerance Is Not the Same as Food Allergy
DAO supplementation should not be used to prevent or treat an IgE-mediated food allergy. Food allergy involves a different immune mechanism and can cause serious or life-threatening reactions.
Anyone experiencing throat tightness, facial or tongue swelling, wheezing, difficulty breathing, faintness or a history of anaphylaxis requires appropriate medical evaluation. DAO should never be used as a reason to deliberately consume a known allergenic food.
When DAO Support May Make Sense
DAO supplementation is most logical when symptoms have a fairly reproducible relationship to meals, particularly foods known to contain more histamine. The goal is not to label every digestive or food-related symptom as “histamine intolerance,” but to determine whether supporting dietary histamine metabolism changes the pattern.
Persistent food reactions deserve broader consideration as well. Gastrointestinal health, medications, alcohol intake, food allergy, migraine, mast-cell disorders and other conditions can overlap with symptoms attributed to dietary histamine.
Hist Arrest or DAO Enzyme 30,000 HDU?
HormoneSynergy® currently carries two RetzlerRx® DAO options for dietary histamine support.*
RetzlerRx® Hist Arrest provides 20,000 HDU per tablet and offers straightforward DAO support before meals.*
For individuals looking for a higher-activity capsule formulation, RetzlerRx® DAO Enzyme 30,000 HDU provides 30,000 HDU per capsule from porcine kidney extract (DAOgest®).*
Neither approach needs to become a permanent solution simply because certain foods cause symptoms. DAO is best viewed as a targeted tool that can be used when appropriate while the underlying dietary and gastrointestinal pattern is understood.
Suggested Use
Take one tablet before meals, or as directed by your healthcare professional.
Because DAO is intended to interact with histamine from food within the digestive tract, taking it in relation to a meal is more consistent with its proposed mechanism than taking it well before or after eating.
Why RetzlerRx®
RetzlerRx® supplements are selected and developed within the HormoneSynergy® clinical environment with an emphasis on ingredient quality, appropriate dosing and clinical usefulness. Supplements are used to support physiology where they make sense rather than being presented as substitutes for diagnosis, food quality, exercise, sleep or medical care.
That approach is discussed in more detail in Supplements Are Tools, Not Miracle Cures and The Practical Longevity Supplement Stack.
Frequently Asked Questions
What does RetzlerRx® Hist Arrest do?
Hist Arrest provides supplemental diamine oxidase to support the breakdown of histamine from food within the gastrointestinal tract.*
How much DAO is in each tablet?
Each tablet provides 20,000 Histamine Degrading Units (HDU) of diamine oxidase.
When should I take Hist Arrest?
Take one tablet before meals, or as directed by your healthcare professional.
Does DAO lower histamine throughout the entire body?
Oral DAO is primarily intended to support the metabolism of dietary histamine within the digestive tract.* It should not be viewed as a systemic antihistamine.
Is DAO the same as an antihistamine medication?
No. Antihistamine medications generally block histamine receptors. DAO is an enzyme that helps metabolize histamine within the gastrointestinal tract.
Can Hist Arrest be used for environmental allergies?
Hist Arrest is formulated around the metabolism of dietary histamine. It should not be presented as a treatment for pollen, animal dander or other environmental allergies.
Can DAO prevent a food-allergy reaction?
No. DAO should not be used to prevent or treat an IgE-mediated food allergy or anaphylaxis.
What is the difference between Hist Arrest and RetzlerRx® DAO Enzyme 30,000 HDU?
Hist Arrest provides 20,000 HDU of DAO per tablet. RetzlerRx® DAO Enzyme provides 30,000 HDU per capsule and uses porcine kidney extract (DAOgest®). Both are designed to support the metabolism of dietary histamine within the digestive tract.*
Where can I review the complete product information?
For additional ingredient, direction and research information, view the Hist Arrest product information PDF.
HormoneSynergy® Longevity Medicine
Portland • Lake Oswego • Oregon
Evidence-Based Preventive Longevity Medicine
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.