The Antihistamine Protocol

I thought I knew everything there was to know about ttc and recurrent pregnancy loss. Then a friend of mine told me it might be worth looking into the Antihistamine Protocol because of my history, and I had to admit that I had never heard of it.

Initially, I ignored her advice. But when she asked again what I thought, I decided to read about it. And I’m actually glad I did.


NEVER take medications without doing your research and/or consulting your doctor. I am not a doctor, I simply do a lot of reading.


The Antihistamine Protocol is a non-proven approach to enabling implantation in women who have had issues with this part of the process. With three early chemical pregnancies under my belt, this sounds like it could be me.

This protocol has been used on women attending some fertility clinics, but there is very little information on the internet and only anecdotal evidence that it is successful.

The theory is

Implantation may fail because of immunological issues – the body essentially rejects the fertilized egg.

The protocol in a nutshell is

From 3 days past ovulation (or 2 days before transfer if you are using assisted conception),  you take:

1. Claritin
10mg daily

2. Pepcid
20mg twice a day (be aware that this is double the recommended normal dose)

3. Prednisone  (this is often substituted with Benadryl – see why this is WRONG below)
10mg daily

I have been unable to find any clear guidance on when you stop taking these.

The ideal result

The protocol dampens down the body’s immunological response and allows the egg to implant successfully.

The Antihistamine Protocol

The body has FOUR different histamine receptors, which play a part in your normal immunological responses. They are known as H1, H2, H3 and H4.

H1 and H2 are the receptors that this protocol targets.

Claritin (drug: loratadine) targets H1.
Pepcid (drug: famotidine) targets H2.

Prednisone is a steroid that suppresses the inflammatory response. It carries a risk of dependency if taken for more than 7 days. It is also a prescription drug with a long list of side effects.


I have seen multiple accounts of people substituting Benadryl for prednisone (prednisone is a prescription drug). You DON’T want to do this. Benadryl targets H1 receptors. You are already targeting H1 with Claritin, so there is no need to add Benadryl to this mix. It is simply unnecessary (and it has a bunch of side effects, is not recommended in pregnancy (Benadryl is sometimes recommended in pregnancy), and will make you fall asleep).

My opinion (for what it’s worth)

If you have a history of chemical losses, I think taking Claritin in the second half of your cycle is worth a shot. And in fact, I will be doing exactly that this month, as a personal “trial”.

Benadryl is simply doing the same job as Claritin, with more side effects. I’d leave that alone.

Prednisone just seems like a terrifying medicine to me – in fact I threw away a pack when my son was small instead of giving it to him. The doctor prescribed it for a difficult chest infection, but after I read the enclosed leaflet I decided things weren’t bad enough to warrant him taking it. The fact that stopping it suddenly can be dangerous if you’ve taken it for more than a week was also unnerving to say the least! I would only ever take this under a doctor’s supervision.

As for Pepcid, it is primarily a stomach acid reducer. It won’t do you any harm, but personally I am not convinced enough of its effectiveness to take it as an aid to implantation.

Things to think about

There is one thing that everyone seems to overlook with regards to this protocol, and that is the fact that there is no proof at all that you are rejecting healthy eggs.

What if you’ve had seven early losses and it is simply because your body is doing its job in rejecting non-viable eggs?

What if some other sub-clinical health issue is affecting your egg maturation and egg quality but the miscarriages are the only symptom?

In my case, would I want to suppress my immune system to fool my body into accepting an egg that would later fail anyway?

This is a big question.

I’ve had miscarriages – I know how it feels like your body is conspiring against you. That may not be the case.

Why I think it might help me

I had a blood transfusion 17 months ago, and since then I have had three losses at 4 weeks. Every other cycle has been a BFN.

Before my blood transfusion I got pregnant 5 times out of 9 tries. I had two children and three miscarriages. But the fact is I was getting pregnant ALL THE TIME. I had a 55% success rate on any given cycle.

But all I’ve had since the day of my blood transfusion is faint positives for a couple of days and endless heartache. I genuinely think I have some kind of immune response that will not allow an egg to implant.

Oh, one other irreverent fact – I haven’t been ill once since the blood transfusion. Not even a cold, or a runny nose. My family had the vomiting bug twice and it didn’t affect me. My husband gets everything the children bring home from nursery. I get nothing. My health has never been so robust. Seriously! I am impervious to germs.

Now, I know this is a ridiculous thing to base any kind of judgement on, but… it’s weird, right?

I had a blood transfusion.

My ability to get pregnant straight away disappears.

My endless coughs, colds and fevers disappear.

I may be adding two and two and getting five, but just in case I’m not, I’ll be taking Claritin this cycle.

Just in case.

Useful links:

A very detailed post on immunological research. Information on the protocol is about half way down under “CCRM’s anti-inflammatory/anti-allergy cocktail”

From the Braverman fertility clinic: A warning that using histamines may negatively affect implantation.

6 thoughts on “The Antihistamine Protocol”

  1. Wow really interesting. I think I’m having implantation issues too. I’ve been taking some stuff from naturopath to help and it has extended my cycle by 1-2 days which is good. I’m convinved I should fall after that…grrrrrr

  2. This is really interesting. Did any of your research mention Allegra? That’s what I take all year to control my allergies, though it’s on the list you should take while pregnant (I stop taking it whenever I have known or thought I may actually be pregnant), so perhaps it’s not part of the protocol. Just curious,though. From a purely anecdotal perspective (I’m not a doctor), I would steer clear of Prednisone altogether if there’s any way to avoid it. I was on it for a while quite a few years ago and it was not a pleasant experience. Be very careful with that one. Keep us posted on this! You’ve piqued my interest!

    • Hmm, I didn’t see anything relating to Allegra but a quick search shows it also acts on H1 receptors (like Claritin and Benadryl). I wouldn’t take anything contraindicated for pregnancy either. I won’t be touching prednisone – too scary! Just good old Claritin for me 🙂 I don’t hold out much hope, but you never know, it could be the one thing that tips the balance in my favour.

  3. I followed an antihistamine protocol after having 3 chemical pregnancies and a 9 week loss (blighted ovum). I used Benadryl in my protocol, it was: 1 Claritin + 1 Pepcid AC in the morning, and 1 Benadryl + 1 Pepcid AC at night. I took it until I was 8 weeks pregnant, because before that, every time I stopped, I would start spotting. I am currently 16 weeks pregnant and everything looks great with the baby so far. I agree with you that people should always consult their doctors and do their own research, but I wanted to share my own experience.

    • Thanks for sharing – I have been wondering how long to take the meds for if you get pregnant, so that is really helpful. I’m sorry for your losses. Congratulations on your pregnancy – it must be wonderful after everything you have been through x

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