Thyroid UK
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Levo and Carbimazole lowers digestive Enzymes?!

So I was recently diagnosed with low DAO enzyme (the enzyme needed to break down Histamine in the gut). I have had stomach problems all my life but seems like my reactions have gotten more severe since starting Levo over a year ago. Then I did some research and found this study where they found that levo and carbimazole both lower MAO and Histaminase (DAO) in the gut (in rats).

So was I Histamine Intolerant before starting Levo? Or did Levo do this to me? My DAO reading was so low that it didn't even register in the range, was given PPI and told to take antihistamines for life!?!? What came first the chicken or the egg?

Does anyone else have any information on this? I could only find this one report. I know DAO is rarely ever tested, so what do you think? There's a chance this medication is causing gut problems or at least is worsening them in thyroid patients.

27 Replies

All 'googled'

Apparently, the DAO enzyme is dependent on B6, B12, iron, copper and vitamin C to stay at a good level.

Diuretics, hormone replacement drugs, vibrates and statins (and others) deplete those levels leading to DAO enzyme being low.

SIBO, leaky gut, Genetic polymorphisms in DAO enzyme can alter DAO production.

Another site (add to above list!) Non-steroidal anti-inflammatory drugs, Antidepressants, Immune modulators, Antiarrhythmics, Antihistamines, Histamine can alter levels.

So, you may have been low in Vits/had gut issues or been on any number of medications that have caused this.


I am only on Levo and T3, I have never in my life been on any other medication. I was low in vit D which I've been supplementing for a year now. Ferritin is not great, but I do take vit C, and was supplementing B12 also before this diagnosis.

I do know very well of all the things that can lower DAO since I have to be very careful now what I intake, but this is the first time I've found a clue that levo could be a DAO lowering substance.

Did you see in the link I shared they mentioned that there is a "significant" correlation between thyroid hormones and the levels of these enzymes?

I personally believe that yes I most likely didn't have a normal DAO count to begin with, but I wonder how much of an affect Levo has on the regular individual? Is it possible it can take a person with normal DAO levels and turn them Intolerant to histamines?

Personally I had some minor reactions before starting Levo, but since having this medication Ive become much more sensitive to certain foods than I ever was before.


What if you are sensitive to fillers and binders in levo? That could also result in poor digestion as you have ongoing allergic reaction.

Is it possible to try different brands?

Maybe you are sensitive to lactose which causes inflammation even though the amount of lactose is quite low.


Hey Justiina! I don't think I'm sensitive to Levo itself. My reactions are totally food related and since I've learned about my histamine intolerance and getting a lot of info from you I've gotten a better handle on my diet and my reactions. I'm actually eating more foods now than before and my reactions have become annoyances rather than debilitating.

What I'm mostly shocked by is my DAO result when I was diagnosed, the result read <2.0 when the range is 14-33. This means my DAO is so low it wasn't even read on the test since their starting point is 2.

This is apparently a pretty big deficiency in DAO which would totally make sense considering the reaction I had that led to my diagnosis. However, while I had reactions before starting Levo none were ever as severe as the more recent ones. So I'm wondering how much of an impact the Levo had specifically on my DAO count, maybe I was more able to break down Histamine before, and this medication has now taken what was left of my DAO, I'm wondering if switching to NDT would help raise my DAO.

So I'm really looking for other research that has been done specifically on how thyroid meds affect digestive enzymes, I feel like this may be an area that hasn't been well covered.

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I am not saying it couldn't be true that levo lowers digestive enzymes, but the mechanism is unknown. Levo can cause SIBO which would naturally cause similar symptoms. In that case it could be for example fillers and binders.

From my point of view your options are

A) try another brand of levo

B) try NDT

C) supplement everything needed to increase DAO

I can't remember if you take digestive enzymes already?

I have berm taking enzymedica basic for four years now. Works well for me. Don't need them every day anymore as I have managed to heal my gut slowly.


Bah! I wish the mechanism was known 😓. I'm a very scientifically minded person and I want the data hehe. I also want something I could show my Endo, because I am open to switching brands or trying NDT if it could actually make a difference, but I feel like I would prefer to show him something to make my case for it.

I don't yet take digestive enzymes. I also stopped taking a multi-probiotic because I learned some strains increase Histamine production, while others lower them. So right now I'm searching for the right probiotic strains, and also a good digestive enzyme (still lots to learn).

Is the enzymedica basic recommended for Histamine intolerance? Or just a good all around digestive enzyme?

Also (a little unrelated) I couldn't take the brain fog from the antihistamines anymore, I also had a hard time getting them on prescription. So I decided to stop, my brain fog is better but I've been getting a lot of random heart palpitations since I stopped, do you think this is related to stopping the antihistamines? My FT3 is also kinda high so it could be that too...


I am the same, I need some evidence and something to lean on, I need to understand it all. Thats why healing has been super hard for me.

I do not know if enzymedica is good for dealing with histamine, but for me it works, so I guess it does help somehow. There are a lot of different products they offer, but for me Basic is the best. I used to use Gold, but its so potent I got blood sugar issues, so I switched to basic. But Gold helped to relief the irritation in the first place. I did a lot of research before I ended up using their product. For some it doesnt work , but then one doesn't have lack of digestive enzymes.

Too bad antihistamines doesnt work for you very well. Some Finnish suffering from histamine intolerance use Lomudal Gastrointestinum and Ranixal with success.

Have your eosinophilic count been retested? As if it isnt sign of anything malicious it could be this :

I had my eosinophilic count re-tested and it was higher than it was two years ago, but not high enough too be a sign of anything serious, we agreed with my doctor that it must be allergy as I had had another episode of hives just before testing.

Probiotics for lowering histamine :

Bifidobacterium infants

Bifidobacterium longum

Bifidiobacterium breve

Lactobacillus reuteri (raises histamine in the short term but elevates anti inflammatory cAMP levels) Lactobacillus plantarum (lowers/inhibits tyramine and putrescine but no effect on histamine)

Neutral strains :

Lactobacillus acidophilus, Lactobacillus Lactis, Lactococcus Lactis, and Lactobacillus plantarum


Lactobacillus casei (produces histamine and tyramine)

Lactobacillus Bulgaricus (increases histamine alone)

How high your ft3 is? It could definitely cause palpitations.

Good if you have been able to try more food, this is sort of grey area, where you go by trial and error, its frustrating as it is not widely researched and patients are often left alone!

I would recommend to try Enzymedica digest , you can probably get it from any health store around there, buy a small bottle first, smallest contains 30 capsules, it is not super expensive so if it doesnt suit you, you wont lose a lot of money! Go to their webpage and learn about the products first as there are so many different type of products, some might be more beneficial for you. I have not tried other products.


Ouch... I read that link you sent, it may not be malicious but it sounds like similar symptoms and another auto-immune condition I don't want to be diagnosed with 😖.

I really do need to re-check my eosinophil count, can you believe not a single doctor even brought it up with me? The reading was outrageously high! And lately I've been getting results with under range blood counts (HCT, Platelets...) no doctor is saying anything! To be honest I have been quietly freaking out about it. I'm going to a new gastro today to make an appointment, I hope I can get it soon. If not I will see if my GP can run these tests again. I would also like to see my DAO tested again because I don't know how accurate that test is.

When I get home from work tonight (if I have enough energy) I will finish my research into enzymes and probiotics (thanks to your help) and will finally order them.


Yes your eosinophil % IS high as mine is just 12 % . So above the range but low enough to rule out many illnesses.

Also your pancreas elastase number was relatively low as I have understood it should be somewhat close to 200. Unfortunately no range was provided but I have understood it's global number.

That can be fixed by supplementing. If it doesn't help then no need to continue as other factors might mess up elastase test result.

There are several things unbalanced with your system, finding the cause would probably help settle down everything.

You are a living human puzzle and we need to find the first piece where to start building the picture :D

It's like peeling an onion layer by layer ruling out possible causes. I am quite sure eventually everything makes sense and even though you'd still have the illness it can be controlled and your life gets easier.

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Thanks Justiina! You're right, either way I don't plan on giving up on figuring things out and hopefully solving the puzzle. Thanks again for all your help!

By the way I'm not sure if you showed me this or if I found it myself (brain fog), but just in case have you seen this incredible food list?:

There is so much detail it's unbelievable, almost every food I could think of was on there including Histamine content, and if it is a liberator, blocker, or quickly perishable. (You've probably seen it but I'm putting it there just in case).

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!!!!!! Had not seen that list.

I had NO idea iodine is histamine liberator. No wonder I can't tolerate it well but it also makes it hard for me as I can't supplement so :(

It also list buckwheat high in histamine, but I tolerate buckwheat very well as well kiwi, raspberry and strawberry.

But what caught my attention was artificial colours. I have always had troubles with certain type of red. I often end up having huge blister on my lip. I thought it was herpes but doctor said it can't be as it heals after popping the blister. But it can be huge lump on my lower lip half inside the mouth and half visible and always after eating certain type of red candy, yoghurt or so.

Thanks for that list!!!!!


You're very welcome!

I have reacted to buckwheat pasta twice. It was such a delicious pasta and I still have some more left. I bought some Daosin last week and haven't tried it yet, I'm thinking of testing by taking some before the pasta. From what I read it makes it possible to eat high histamine foods.


Yeah daosin should make it possible for you to eat food high in histamine.

You should try it!

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I'm going to do it this week! 😊 I keep putting it off as I'm nervous to get sick again, but my girlfriend keeps begging me to do it since she sees it as the magical pill that will allow me to go out to restaurants again.


But you can try it with any meal, you don't have to test with food you know gives you very bad reaction. Try something you know gives you mild reaction.

I understand your girlfriend, but I hope she is patient as it isn't magic pill that way, it can take time before it settles down.


She's a pretty patient person to put up with me haha. I was thinking of the buckwheat because I reacted to it both times, the reactions were severe enough that it was obviously from the buckwheat, but not so bad that I was incapacitated. Also it was just so delicious I've been thinking of it ever since!

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I bet she is and just want you to feel better and be able to enjoy life :)

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Something just struck me so haven't had time to think itcthrough but you are saying that it could be the Levo doing this as this is the only change but the fact that you have been diagnosed with a thyroid problem then that's a huge. Hangs as well so which came first to upset the apple.cart? Could well be the hypothyroidism.


Well the study shows that thyroid hormones impact MAO and DAO enzyme count, my theory is that if you are lower in hormones (more hypo) you'd have more DAO, since the study shows that as they increase hormones the DAO count goes down. Note in the study they use Levo and carbimazole, probably injected in the rats, so direct hormones.

So I'm fairly certain that even tho I am hypo, and low stomach acid, etc that yea I had digestive problems before the Levo. However this recent result of mine would indicate that I now have zero DAO left in my gut. I really doubt this was the case before starting Levo.

So my assumption is that it's a mixed thing, where I was already low, and this only made it worse. BUT... if this research is correct then these drugs would take both hypo and hyper patients and make them more intolerant to histamines in food, therefor causing reactions and inflammation in the body, which drives further destruction to the gut...

Which I why I was blindly hoping someone else had some research on this... seems like it doesn't exist however.

I've been reading a lot of members on the forum complaining about stomach issues and allergic reactions that are related to histaminosis, however most of them never heard of the term, neither did their doctors. But from the symptoms it's clear that they are speaking of Histamine intolerance. I think this is actually very common in patients (yet genetically speaking it's quite rare to have low DAO), so I think it's gotta be the meds. Since it seems nobody else is being tested for these enzymes I am willing to be the lab-rat, but I'm hoping to find someone else on this forum who has also gone through these tests (hopefully before and after starting meds).


Thank you for explaining more fully, it was just a thought that flashed through my mind!

On the subject of PPI's I was prescribed them without even complaining about anything. I had a hoarse voice which I now realise was thyroid related so hospital put a camera down but couldn't find anything wrong but as a double check was sent forca barium splash!

Nothing found there though until they pressed rather hard on my stomach and decided I had reflux and prescribed PPI's. Didn't make any difference but then I read up about them and weaned myself off them. Apparently they are addictive so you must never just stop them. I was fine after and suspect the induced acid reflux was a slack sphyncter due to being under medicated.

Just over a year ago I had my second hip replacement. But I was continually sick for a week after. Turned out it was the pain medication which was new to me but they wouldn't let me try any other I knew I was ok on. One day they said I was to take a PPI. I refused and gave my reason that as a thyroid patient I was probably low on stomach acid so I was asked if it had ever been tested. Well I haven't so lost my argument. She stood there till I took it. About 30 mins later my breakfast reappeared. If I had vomited into a China bowl you would happily have eaten it. It had t broken down at all. It was porridge with a little bit of ham omelette along one edge. I only ate one mouthful of than. No sign of any breakdown and it came back while which was extremely painful!

After my complaint to the hospital the only apology I got was that there were sorry I had been given it within 4 hours of my thyroid meds, not that I shouldn't have been given to me in the first place!

Look into the harm they do and think carefully about continuing. I've read on here that apple cider vinegar is a good alternative but never needed it myself.

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The thought flashed through my mind too! I very much appreciate your input.

Those darn PPI's I also only did worse on them, and had a harder time digesting foods once I stopped taking them than before starting...

They don't consider that low stomach acid could cause problems, they always assume it's high stomach acid.

I've learned that no doctor knows everything, luckily I have a knowledgable Endo who is actually interested in my gastro diagnosis and always asks to see my results. But there are some things that even he doesn't seem to know. I've been racking my brain over how to make a change in this medical industry.

I'm 31 years old and I have made it my plan to really change the medical field's understanding of Hashimoto's, I'm willing to spend my life doing this. So I spend hours looking at studies, trying to piece together the puzzle, using myself as a lab-rat and paying out of pocket for all sorts of tests.

I hope that I can make some sort of difference, and I'm hoping I can get the help of some people on this forum. We tend to complain about our doctors, but what we need is actually less of a division between patients and doctors, it's up to us to change their mind, I don't think they're gonna do it on their own.

Sorry for the ramble, but after reading your post it really boiled my blood. Just the thought of how many thyroid patients go through he experience you described on a daily basis...


That's all we can do really and that's why I thing good forums like this one are so important. We can share the good and the bad and hopefully push the good forward. I posted the other day about asking about a drug I've been given after Letrozole and my NDT. I spoke to a pharmacist at the cancer hospital and she wanted to know how I knew about T3 so I explained that and yes the tests are the same if taking T3 but the results are read differently. She was really interested and thanked me for telling her that so I think if we can educate others along the way then that has to be a positive thing and who knows but hopefully one day it will make a difference!


I agree with you. It's great that you're sharing your knowledge. My GP is also very open to learning more about Hashimoto's from me, once he was unable to help me on Levo alone he referred me to Endocrinology and actually asked me to come back with more information that could help him treat and diagnose future patients. But I think doctors like him represent a minority.

I guess we'll just keep pushing on through! I've only been researching for a year now, this forum has helped me learn a lot very fast. But eventually I want to compile all the research and try to see if I can work alongside the medical industry, maybe campaign to fund some studies, find doctors who are interested in alternatives. It sounds hard but I think with the help of members on this forum we could really do something. There's over 50,000 of us! Hope I'm not dreaming too big...


Typical so you're low on some enzymes and the doctor gives you more drugs. PPIs like Omeprazole will make everything worse. They reduce stomach acid and are only needed if you have an ulcer. We need stomach acid to digest food and absorb iron, B12 etc.

A functional doctor told me that prebiotics and probiotics will increase histamine so best to avoid those things.

As for digestion I've been reading Izabella Wentz's new book Hashimoto's Protocol which explains the amazing connection between our gut and liver and how vital it is in converting T4 to T3. Many people with Hashimoto's disease or thyroid issues lack the necessary enzymes. Systemic enzymes supplements like Wobenzym can massively help. I'm researching this area at the moment. I know you can also buy plant based enzymes too. Many diet based interventions can also help.

Please, please focus on the original problem and avoid taking more drugs which will introduce more side effects. PPIs are terrible drugs especially.


Oh trust me I wasn't a fan of the PPI and I am very adverse to taking drugs. I even stopped the antihistamines because I can't gauge my diet while I'm on them and they cause brain fog.

I needed the PPI because I did have ulcers (probably still do) was diagnosed with UC and duodenitis.

I try to use apple cider vinegar before eating meals I know are hard to digest, it works, but once again it's high in histamine so I end up with migraines and other problems.

I'll take a look at the book you mentioned as I am also now researching enzymes and supplements that could help.

About the probiotics, actually there are certain strains that increase Histamine and other strains that lower them, so for someone with DAO deficiency it's important to use single strains whereas other people are recommended multi-strains, take a look at the reply Justiina made in this post, she's quite knowledgable in this subject.

Thanks for having my back about not taking more drugs, and for all the info you've provided. Sometimes all this research leaves my head spinning hehe!


I know what you mean about head spinning. I've had two bouts of Vertigo over the years that lasted for several weeks. I also feel dizzy here and there anyway. Interesting stuff. I'll have a read and all the best! Thanks.


Oh that doesn't sound fun.. I get vertigo from time to time in really quick short spurts. I can't imagine what a several week episode would be like.

Thank you too and all the best!


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