November 19, 2014 9:00 pm


The connection between antidepressants, brain fog, and histamine intolerance is poorly understood.

Specifically, histamine intolerance commonly leads to medication issues. Does histamine intolerance cause medication intolerance, or do medication intolerances trigger histamine intolerance in some people? We do not know. 

However, we do know that:

  • Certain DAO genes are associated with medication intolerances.
  • Several medications release histamines and block histamine-degrading enzymes.
  • Cytochrome P450 medications (including antidepressants) cause histamine to be released by mast cells.
  • Many medications target mitochondria, essential in regulating cell and mast cell function.
  • Some medications impact the microbiome, which regulates brain function.

Beyond that, researchers still need to do more research. Without clinical trials, we rely on clinical observations from medical professionals working on the cutting edge of clinical practice.

Therefore, this blog post examines the medical hypothesis of Professor David Healy, a psychiatrist and pharmacologist with an active interest in adverse drug reactions to psychotropic drugs.

Additionally, I have expanded it to include my observations based on hundreds of autonomic response tests within my client base.

antidepressants histamine brain fog

Antidepressants and Histamine Destabilisation

Professor Healy states that many antidepressants are not “clean” but rather interfere with the histamine system.

Specifically, antidepressant withdrawal can be viewed as a “histamine over-activity (semi-allergic) state,” which arises because the person has been on antihistamines chronically.

Indeed, this hypothesis aligns with the emerging theory that the antihistamine system is usually a tightly controlled process. Specifically, H1R and H4R are pro-inflammatory and initiate an immune reaction, while H2R and H3R are anti-inflammatory and halt an immune reaction.

For example, long-term antihistamine use likely alters the equilibrium of this tightly controlled immune system, potentially triggering IgE allergies and food sensitivities, which are common with antidepressants.

Therefore, Professor Healy’s protocol for antidepressant withdrawal includes tapering off the medication with antihistamines and mast-cell stabilisers to compensate for this dis-equilibrium.

How Genetics Influence Antidepressant Tolerance

In his “Guide to Stopping Antidepressants,” Professor Healy writes:

“A small number of people have a severe ‘toxic’ reaction to SSRIs with neurological and other features often starting within days of beginning treatment. The after-effects may endure for months or years. These drugs, in the doses they are usually given, are grossly overpowered. It’s like a huge articulated truck travelling down a stone-walled country lane.”

This suggests that the ability to detoxify or methylate medications is important for managing histamine intolerance.

Although Professor Healy does not expand on this point, I want to clarify that a simple lifelong DNA Dose test can determine your bio-individual genetic response to antidepressants.

Moreover, Professor Les Sheffield from DNA Dose concludes that only 50% of people have a normal response to antidepressants, 40% need their dosage adjusted, and 10% cannot metabolise them at all.

Pharmacogenomic testing is highly recommended prior to commencing antidepressants.

histamine intolerance, mast cell activation, antidepressants, medicines, alison vickery, health, Australia

Understanding Brain Fog

Adverse drug reactions commonly cause brain fog.

Interestingly, Professor Healy concludes that muscle memory disruption causes brain fog. That is, he believes brain fog originates not just in the mind but in the muscles.

In other words, routine muscle memory activities aren’t happening as they should, leading people to concentrate harder and still make mistakes, mistakenly thinking their memory isn’t as good as it should be.

Despite this, cognitive function testing is likely to be normal because the brain is functioning normally.

Addressing Brain Fog

The solution? Professor Healy suggests staying physically and mentally active to refashion nerve endings.
“Activities such as walking or swimming may help, especially if done in a graded program that ensures daily activity and gradually increases activity levels,” he states.

Specifically, he advises adopting the same approach as people with muscle memory problems, such as playing the piano after an arm or hand injury—getting back to playing and developing another set of memories through practice.

In other words, many of these symptoms arise from interferences with the nervous system response system, which controls communication from the brain to the muscles.

How Medications Affect Mitochondrial Function

Many medications damage the mitochondria, leading to cellular stress and mast cell activation. Researchers have also found that some antidepressants damage the mitochondria.

That is, these drugs can also alter critical nutrients, including thiamine. The brain, a huge energy consumer, often experiences brain fog due to mitochondrial issues.

On ART testing, I regularly see the brain needing mitochondrial support to function. 

Additionally, I have seen mitochondrial dysfunction due to adverse medication reactions completely restored through supplementation after the withdrawal of the medicine.

The only products I have seen achieve this are CarnoMed (sold as Mitochondrial Rescue in the USA), CreGAATine, Komplex Q10, and Karnozin Extra, combined with the LifeWave X39 and X49.

histamine intolerance, mast cell activation, gut dysbiosis, antidepressants, alison vickery, health, Australia

Antidepressants and the Brain-Gut Axis

Importantly, researchers have found that antidepressants have a microbial action, leading to studies on their use in antibiotic resistance.

However, while many studies now focus on their antimicrobial potential, few examine their effects on the whole microbiome

The brain-gut–microbiome axis creates a bidirectional communication pathway between the gut microbiota and the central nervous system.

Indeed, emerging research shows that metabolites from our microbiome regulate brain function.

Are we missing the forest for the trees? If we tended to the microbiome, would we need antidepressants and antimicrobials?


Firstly, the withdrawal from psychotropic medications is exceptionally complicated and should be done under medical supervision.

Professor Healy runs an e-clinic, where he consults on the prescription and withdrawal of anitidepressant medications.

With that said, many medications destabilise the histamine system.

However, a current theory is that when medications are withdrawn, using antihistamines and mast cell stabilisers may eventually restore the histamine system.

Furthermore, addressing the gut microbiome, mitochondria, and cell membranes can also reverse histamine and mast cell activation.

To learn more about how genetics affects our medication choices check out my blog post,  Medicines that Cause Histamine Intolerance

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