Histamine Intolerance & DAO: Answers to Your Questions

So many of you emailed me with questions that I put together a Q&A. This is a far broader topic than I can summarize (even with six hours of writing!), but it’s a start. The formatting is ugly and you’ll have to scroll through a lot of text. I’m prioritizing your access to the information over making it look nice. Expect typos.

I don’t have allergies. Could I still have an issue with histamine?

Absolutely. I don’t have allergies either and have no allergy symptoms. Right now, I can only present myself as a case study and say that I’ve encountered multiple people in forums who are histamine-intolerant and do not have allergy symptoms. This is on my list of topics to investigate and I’ll present real data when I can.

What’s the name of the supplement you use and where can I buy it?

The actual name is Histamine Block and it’s available on Amazon. Histame is probably the most popular DAO supplement. It costs less than Histamine Block, but is also less potent. (Disclosure: If you buy though either of those link, I’ll get a small percentage of the sale.)

What is an HDU?

HDU stands for “histamine digesting unit” and you’ll see it listed on every DAO supplement. It appears to be a scientific term that’s been co-opted for marketing, but the two don’t align. Currently, I only use the numbers to compare the strength of one supplement to another. I’ve also found that, so far, 20,000 HDU is most effective for me.

I don’t get a migraine or headache every time I eat, but I do sometimes and can’t connect it to any particular food. Could DAO help me?

Quite possibly. I think I’m fairly rare to have eating anything trigger migraines (or histamine intolerance symptoms). Far more common is for people to have trouble with particular foods. Certain foods naturally contain histamine or are “histamine liberators,” both of which result in even higher amounts of histamine to your system than is part of the normal digestion process. Most people don’t have as much trouble with the normal histamine release as I do, but run into problems when they eat foods that contain or liberate additional histamine.

What foods contain or liberate histamine?

This is a landmine. The short answer is that you will find many conflicting lists of histamine-containing foods online. Searching forums will confuse you even more. Here’s the list of histamine-containing foods that’s most widely regarded as accurate. You’ll notice that it also includes foods containing tyramine. The two are related (both being amines) and there’s a lot of overlap between them. Tyramine has long been suspected to trigger migraines, and possibly other headaches, so a list restricting both is a good place to start.

Starting an elimination diet is overwhelming and time-consuming and I have tons of guidance to offer. On another day.

Are DAO supplements safe?

Yes, according to the dietician I’ve been consulting with (who is as close to an expert on this topic as you can get), my naturopath, and the recent DAO for migraine prevention study. Any of the DAO that isn’t used is flushed out through the digestive process. It’s not absorbed in any way, nor does it stick around for more than a few hours. (The information in the last two sentences is from my naturopath. I’m going to double-check it with the dietician.)

Do DAO supplements have any side effects?

None of the 117 patients who completed the aforementioned study of DAO for migraine prevention reported any side effects. That’s pretty much unheard of for a study of a drug or supplement. Online forums are a little different (and also not part of a controlled experiment).

The main side effect I’ve seen on forums is that some people say it makes them shaky. That was true for me initially. Taking the DAO only five minutes before I ate seemed to help, I think because it didn’t sit in my stomach for too long without food. I did that a few times before moving to taking it 10 minutes before eating. My intuition is that it is more effective if it has more time to release before encountering food, but I don’t know that for sure. I’ll ask my dietician about it.

Someone just told me that she flushes and sweats when she uses any brand of DAO supplement. That’s the first time I’ve heard of that side effect and I don’t know how common it is.

I sometimes react to natural supplements. Am I likely to react to this one?

I’ve demonstrated so much intolerance for natural supplements that my naturopath only prescribes pharmaceuticals for me(!), but I’m doing fine with this one. Use your own judgment to decide if the risk is worth it for you. If your reactions tend to be severe or you think the risk is too great, consulting with a naturopath or dietician before taking it would be wise.

Where did you learn about DAO supplements?

The dietician and my naturopath both recommend it. It is also commonly used among people with histamine intolerance, so it’s mentioned on forums a lot.

If I have a histamine issue, could I take antihistamines instead?

If your triggers are connected to food or eating, it appears to be more effective to take DAO than an antihistamine. Adding the enzyme you’re deficient in seems to address the problem more directly than an antihistamine. Antihistamines can also cause a strong enough rebound effect that the dietician warns against them. For now, I’m still taking 12 mg of cyproheptadine, a prescription antihistamine used for migraine prevention, each day.

If you do decide to try an antihistamine, patients with histamine intolerance (whether their symptoms are migraine, headache or something else) seem to have more success with older drugs, like cyproheptadine and Benadryl, rather than the newer ones (Allegra, Claritin and Zyrtec). I don’t know why.

What’s “histamine intolerance”?

Histamine intolerance (often referred to as HIT) is when someone has a reaction to ingesting histamine and/or the release of histamine that accompanies digestion. The reactions vary, but can include diarrhea, headache (and migraine) nasal congestion, wheezing, low blood pressure, irregular heart beats, rashes, flushing, and itching.

Histamine intolerance isn’t a food allergy, but is a food sensitivity (it’s an important distinction). It’s not widely known about, but is starting to get a lot of attention in parts of Europe (especially the U.K.) and Australia. Thanks to the internet, the information is accessible if you know where to look.

For what it’s worth, I haven’t been diagnosed with histamine intolerance, nor have I diagnosed myself with it. But it’s the best search term to find information on histamine and food, and it’s the term most people who have issues with histamine apply to themselves.

Why do you qualify so many statements with “appears to” and “seems to”?

There are a lot of unknowns about histamine and DAO. Finding solid information online is difficult and patient groups lean toward pseudoscience. While I believe I’ve sussed out reliable information, I would rather say I’m not absolutely sure about something than discover that I presented incorrect answers as fact. If I continue to feel as good as I have this past week, I’ll soon be combing through journal articles at the local university library and will pass on what I uncover.

What else do I need to know?

I’m sure I’ll be sharing much more as the week — and year — goes on. If you want to know more NOW (I sure did when I first started learning about this), here are some places to get started:

  • Histamine Intolerance Awareness (website) — The food list on this site is kind of difficult to follow and some of the inclusions are questionable, but the rest of the information is a very helpful start. Genny Masterman, who put this site together, has a book called What HIT Me? It’s a good introduction and is written in an accessible, easy-to-follow style, but I found the meatiest information to be covered sufficiently on the website.
  • Dealing with Food Allergies (book) — This is my favorite book for the general public, even though the title is misleading (histamine intolerance is NOT an allergy). It doesn’t contain a lot of detail, but hits all the important points and has clear, well-organized food lists. Be sure to check the sections on both histamine and benzoates (benzoates are histamine liberators). I think there’s a section on tyramine as well. The author, Dr. Janice Joneja, the dietician I’ve been working with.
  • Histamine and Histamine Intolerance (journal article) — If you’re willing to wade through an academic article, this is the one to read. I’m working on summarizing it, but not sure when it will be ready to post.
  • Other websites — If you come across another website and are wondering how accurate it is, please ask me. I’d like to have multiple sites to refer people to and it would be helpful to see which sites people who are new to this topic find.

Please remember that I’m not a medical professional and nothing on this site should be considered medical advice. I’m a patient reporting on what I’ve learned and experienced. I hope that it can help you with your own sleuthing, but please solicit the input of your health care team.

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18 Responses to Histamine Intolerance & DAO: Answers to Your Questions

  1. Sue says:

    Thanks so much for this Kerrie – much appreciated!

  2. Gail says:

    Thanks so much for this. I have one question, though. Why is Histamine Block more effective than Histame? I looked at both of them, but cannot take Histamine Block because it uses an Ascorbic Acid Vitamin C base (I cannot take this due to a food sensitivity problem I have for another condition – nterstitial cystitis)

  3. You’re welcome, Sue!

    Gail, Histamine Block is more effective for _me_ because it is a higher dose (10,000 HDU per capsule vs. 4,000 in Histame). Some people get all the benefit they need from one Histame. You can take multiple Histame capsules, if necessary, though that would be more expensive than Histamine Block.

    I started with Histame and took more and more capsules to get to the dose I needed. Histame costs about $.80 per capsule, while Histamine Block is about $1. And it takes five Histame to equal the dose in two Histamine Block.

  4. Patty says:

    I have had migraines for 30 years. I thought that after going through menopause they would subside (ten yrs ago) they only increased. I use triptans to fight them, allot of triptans. Here in Ireland you can get them at minimum cost for in our drug scheme. That is still €140 per month but better than the States which is where I am from. Anyway I stopped all caffiene consumption two weeks ago. It was a horrible withdrawal which should tell me something aobut its effect on me. I have also started to eliminate all foods with tryasine. I just saw your article here today and will also include those with histimine. The feeling I always had with my migraine is that they felt like horrible hangovers. Throwing up and all. I feel great without the caffiene and hopefully simplifiying my diet will help enormously. Then maybe I’ll only have to use the triptan once in awhile. Wouldn’t that be wonderful. I also just dicovered the tea Rooibos..had never heard of it before. Its great for replacing the coffee. Thanks for all your time creating this website. Cheers.

  5. Patty, it’s great to hear that you feel great after stopping caffeine. Best of luck with your diet… please let us know how it goes.

    Take care,

  6. Larissa says:

    I saw a new doctor (an integrative MD) today and he suggested I start on DAO, a supplement called M7+ which has digestive plant enzymes, and a low histamine diet. I thought of you!

  7. Paulla says:

    I just starting with a DAO supplement….do you take yours before EVERY meal or only when you feel an issue with symptoms coming on? Id like a preventive approach v. reactive but wasnt sure if taking the supplement prophylactically would be done with every meal or once or twice a day, etc.

  8. Jane Guthrie says:

    Hi Kerrie,

    I have been struggling with figuring out my triggers for 2+ years and am thinking that maybe it could be a histamine reaction. Did your doctor/dietician test you for DAO levels before putting you on the supplement? Or did you just try it to see if it would help? Did you also eliminate all the foods indicated on the mastocytosis site?

    • There is a test for DAO levels, but it is considered unreliable. The level of DAO in a person’s blood may not correspond with the amount available for digestion and there’s no solid range in which to identify what’s normal. Trying a DAO supplement and seeing if it helps provides most people with more evidence than the blood test.

      I have eliminated all the foods on the mastocytosis site, but I had eliminated ALL food before starting DAO (literally, I was subsisting on a formula that’s used in feeding tubes). I just haven’t added anything that’s high in histamine back in permanently. I have tried some high histamine foods, but took more DAO than more normal amount beforehand and I did fine.

      Please let me know what you learn! I hope you find relief soon.

      Take care,

  9. Kerryn Duurland says:

    Please tell me where I can purchase any dao supplements in nsw central coast gosford area

  10. Sarah says:

    Thank you for putting this together. There is one thing that not many people with histamine intolerance consider, and I am interested to know if you have heard anything about it. Histamine is produced by a number of bacteria, and I wonder how much of a role gut dysbiosis plays in this, and whether fixing the dysbiosis is key to reducing the drains on the bodies own supply of DAO. For me, my histamine tolerance has changed markedly at a number of points in my life. I have done the GAPS diet in the past and had much better success at handling histamine. Then I got a weird bug last year and not only do I have a strong response to anything containing histamine or tyramine, but I also have the same response to protein, any type of protein, fresh or old, nuts or meat. Except the response is delayed by a number of hours. This makes me wonder whether the bug that caused sores in my mouth, was a bacteria that went through to my gut and produces histamine from histidine. Histame really helps control this, but without it, each time I eat protein, I get all the same symptoms that I used to only get for histamine. Postural hypotension, muscle fatigue (walking up 5 steps – and I am active), tiredness, and all the mood problems like shortness of temper, irritability, brain fog, poor concentration and sound intolerance. I also get a very sharp pain under the upper rim of my left eye socket. This is in the same spot that people get cluster headaches from histamine. So I would like to a) find out more about this theory, and b) raise this question with as many people as possible, to see if others have found a similar pattern in their responses.

    Thanks for reading!


    • Thanks for sharing your experience, Sarah. You’ve raised far more questions than I have answers to. People do find that healing their guts helps with histamine intolerance, though I don’t know exactly how they do it, since GAPS foods are pretty much the antithesis of low-histamine.

      How frustrating that you’ve developed a new protein reaction. I don’t know if a virus can impact histamine reactions or impede protein production in some other way. The dietician I consulted is fantastic and does Skye consultations — she may be able to answer your questions. Let me know if you want her name.

      Do you have migraine? Your symptoms, including the eye pain, sound very migraine-like. I’m not sure what the protein connection there would be either, but a diagnosis might help you sort things out.

      Best of luck!


  11. Judy Sizemore says:

    The first website I came across was which has great information.
    I also like and I have found it to be very valuable.
    Thanks for all the time and energy you put into research and writing. It’s so helpful!

  12. Diane says:

    I can’t thank you enough for publishing this information. I have had migraines since the age of 7 and have followed the tyramine diet for the last 20 years but still have debilitating chronic dailies. I am convinced that histamine now is the problem and i will try this. But I also have serious upper gastric pain and nausea and i wonder if you had any problems with this also? (the g.i. doc can’t find anything wrong, go figure?) I am hoping this will disappear once i eliminate the enormous remaining number of foods i have continued to eat all these years???
    I will also try a DAO. thanks for helping me, I will let you know what happens.

    • Diane,

      Nausea and abdominal pain are both migraine symptoms, so whatever helps the migraine could help those symptoms as well. I had nausea intermittently until the migraines got really bad, then it became constant. It’s very rare now for me to have nausea.

      Please do keep us posted!


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