A Bio-Individual List of Histamine Inhibitors

This blog post outlines a list of bio-individual histamine inhibitors. It is a companion post for my previous post on the bio-individual triggers of histamine intolerance.

Histamines are a natural chemical in plants, animals, and humans. The body needs histamines to perform critical functions.

The body was designed to be in a state of homeostasis so that the supply of histamine meets the body’s metabolic needs.

Excessive amounts of histamine are normally de-activated by diamine oxidase (DAO), histamine methyl transferase (HNMT), and monoamine oxidase (MAO).

Where the amount of histamines, exceeds the ability of DAO, HNMT, and MAO to degrade the excess, a toxic level of histamine enters circulation, and causes metabolic chaos™.


A November 2015 study found that DAO deficiency remains the leading cause of histamine intolerance. 70% of all persons who responded to a low histamine diet had DAO deficiency.

DAO is a key enzyme, concentrated in the small intestine, and involved in the break-down of ingested and bacterial histamine.

DAO deficiency can be genetic or acquired. Key factors which affect DAO function are:

– DAO genetic inheritance
– DAO inhibiting medications (including long term NSAID use)
– DAO inhibiting alcohol consumption
– DAO inhibiting estrogen (to progesterone) imbalances
– DAO inhibiting gastro-intestinal diseases (including irritable bowel syndrome, crohn’s disease, and ulcerative colitis)
– Bacterial imbalances; as bacteria regulates histamine synthesis
– Nutrient deficiencies: Vitamin b6, vitamin c, zinc and copper, are needed to make DAO.

General Recommendations:

A lab test for DAO deficiency, immediately before, and after a 14 day low histamine diet, is used to diagnose DAO deficiency.


HNMT is a key enzyme concentrated in the liver which is responsible for degrading histamines generated as a result of the functions of the body and in particular mast-cells.

HNMT deficiency can be genetic or acquired. Key factors which affect HNMT function are:

– DAO Deficiency
– Bacterial imbalances (as only around 50% is degraded by DAO)
– HNMT genetic inheritance
– HNMT inhibiting medications
– Mast cell degranulating estrogen (to progesterone) imbalances
– Mast cell degranulating foods
– Mast cell activation disease
– Impaired HPA axis
– Impaired methylation and/or liver function.

General Recommendations:

A 24-hour methyl histamine lab test is used to determine HNMT function.


MAO is a key enzyme concentrated in the brai n which is responsible for degrading histamine and modulating other neurotransmitters; including serotonin, dopamine, and norepinephrine.

MAO deficiency can be genetic or acquired. Key factors which affect MAO function are:

– MAO genetic inheritance
– MAO inhibiting medications (and illicit drugs)
– MAO inhibiting tyramine foods
– MAO inhibiting smoking (inhibits up to 30%)
– MAO inhibiting estrogen (to progesterone) imbalances
– Nutritional deficiencies; particularly Vitamin B2 and iron.

General Recommendations:

23andMe™ can determine the probability of MOA enzyme mutations. An organic urine amino acid test may also be relevant to determine the actual level of neurotransmitters.


The health status of the individual plays the greatest influence on the function of DAO, HNMT, and MAO and accounts for the significant differences in histamine tolerance.

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  • Philip Clax

    Thanks for this Alison, a very useful and thorough analysis. I am homozygous for MAO so I suspect this as well and many other factors have created my histamine intolerance. I wish I could afford any of those tests but unfortunately I have to do my own trial and error with supplements and food.

  • Betsy De Gress

    curious re: neurotransmitters. Most people I read say they find the urine amino acid test to be fairly useless and inaccurate…any thoughts from down under?

    • Hi Betsy that has not been my experience and certainly it would depend upon what you are hoping to achieve and also the skill of the practitioner in interpreting them.

      • Betsy De Gress

        thank you Alison..I just discovered your blog today, really enjoying it. I’m waiting for 23andMe results..I plan to keep in touch!

  • Rebecca O’Callaghan

    Hi Alison, thank you for this article, you have given me such insight over the past year in how to deal with my histamine issues, thank you so much. I just found out that I have am hymozygous for the A1298C mutation (another piece to the never ending puzzle – I’m wondering if there is a reason why you don’t seem to touch on this mutation as much as the other MTHFR mutations? There seems to be a lot more information on the web about C677 Mutations, are different protocols needed? And what makes them so different? Many thanks for your help, Bec

    • Hi Bec thanks for your kind words. It is not intentional; it is just such a big area, and I have not had time to delve into it., on this blog. I also believe there is so much hype around it to be honest. Not that it is not important (cause it is) just that everyone is talking about it. I have not had time to write about it in more detail.

      • Rebecca O’Callaghan

        Thanks so much for getting back to me Alison! I should have said that it’s not just you that seems to have more info on the other mutations, but just on the web in general there seems to be a lot less on the A1298C. Thanks again, and have a lovely day! Bec

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  • Krishna

    Thank you for this wonderful well researched post. I have a question on turmeric. I read turmeric lowers histamine and stabilizes mast cells, but somewhere else I also read turmeric inhibits DAO too. I was wondering what your thoughts were on this contradictory action?

    • hi Krishna turmeric is a mast-cell stabiliser/anti-inflammatory HOWEVER there are other reasons that turmeric may not be well tolerated. For example, if you have phase 1 liver issues it may only be tolerated in very small amounts. Turmeric is also extremely high in Salicylates. Salicylates can also be a problem for people with phase 2 liver (amino acid pathway) issues. I do hope this helps.

  • Bodhi B Wayne

    I am not seeing a list of bio-inhibitors. Please advise.