Some science behind the scenes

Anti-histamines in more detail

Histamine binds to various receptors and there are four histamine receptors in humans designated H1 through H4.  All are G protein-coupled receptors (GPCR).

 

 

Type

Location

H1 histamine receptor

Found on smooth muscle, endothelium, and central nervous system tissue

H2 histamine receptor

Located on parietal cells and vascular smooth muscle cells

H3 histamine receptor

Found on central nervous system and to a lesser extent peripheral nervous system tissue

H4 histamine receptor

Found primarily in the basophils and in the bone marrow. It is also found on thymus, small intestine, spleen, and colon.

The anti-histamines acting on the H1 and H3 receptors tend to be more likely to give you an experience because they act on the histamine receptors in the brain to restrict blood flow to the brain.

In general they all work via hypoxia.

H1 receptor antagonists 

Classically, “antihistamines produce sleep” – at least the doctors call it sleep, it is actually sedation caused by a lack of oxygen – or coma. Scientists have noticed that “destruction of histamine releasing neurons, or inhibition of histamine synthesis leads to an inability to maintain vigilance”.  You bet it does.  In fact watch a person on anti-histamines and they behave in much the same way as someone who has been poisoned with carbon monoxide or been given carbogen – it is the same end result.

People on anti-histamines get a lot of headaches too – that too is lack of oxygen.

The scientists have also noticed that “It has also been suggested that histamine controls the mechanisms by which memories and learning are forgotten”.  Or to put it more simply, if you deprive the brain of oxygen you erase memory.

Given that the oxygen deprivation is pretty general, because the receptors are to be found in most parts of the brain, other parts of the brain are also affected.  For example,  Ataxia  - a gross lack of coordination of muscle movements is a frequent side effect. “Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum”.

It has been discovered that these H1-antihistamines are actually inverse agonists at the histamine H1-receptor, rather than antagonists per se.  This however has little bearing on their effect.  What does have a bearing is that there are first generation and second generation H1 receptor antihistamines.  Second generation antihistamines do not cross the blood brain barrier, and as such do not cause the very direct affects to the brain which is key in their production of spiritual experiences.

This is not to say that  second  generation H1 receptor antagonists do not have an effect, it is just that the effect is far more indirect and less likely.  They share their mechanism of action with the H2 receptor antagonists

The H2 receptor antagonists

The H2 receptor antagonists can produce similar effects but not directly, the effect is indirect via constriction of blood supply in general which then leads to restriction to the brain.  Overall it is less likely that any H2 receptor antagonists will produce hallucinations, however, they do have some other effects.  Libido loss and erectile failure can occur following histamine (H2) antagonists such as cimetidine and ranitidine. 

H2 antagonists, like H1 antagonists, are also inverse agonists and not true antagonists. H2 histamine receptors, found principally in the parietal cells of the gastric mucosa, are used to reduce the secretion of gastric acid, treating gastrointestinal conditions including peptic ulcers and gastroesophageal reflux disease. 

H3- and H4-receptor antagonists

In general these are experimental agents and do not yet have a defined clinical use, although a number of drugs are currently in human trials.