The following medications listed are available in oral or intravenous formulation. Not all medications are available in the US or Europe. Topical and inhaled medications are not included in these lists.
H1 antihistamines interfere with the action of histamine at the H1 receptor. This can help with many symptoms, including flushing, itching, hives, burning skin, nasal congestion, sneezing, constriction of airway, shortness of breath, GI cramping, diarrhea, gas, abdominal pain, tachycardia, blood pressure variability or dizziness. What symptoms are best alleviated varies with the medication; they do not all address all symptoms equally.
|First generation||Second and third generation||Atypical antipsychotics|
H2 antihistamines interfere with the action of histamine at the H2 receptor. This helps mostly with symptoms affecting the GI tract, such as abdominal pain, nausea, and diarrhea. To a lesser extent, H2 antihistamines can decrease vasodilation.
There are few H3 antihistamines and for this reason, their exact effects are largely unknown. However, in research, H3 antihistamines modulate nerve pain and may normalize the release of several neurotransmitters, including serotonin.
The only medication with known H3 activity available for patient use as an antihistamine anywhere in the world is betahistine. It is anti-vertigo drug used mostly in treatment of Meniere’s disease and other balance disorders. Betahistine actually increases release of histamine and for this reason has been associated with the risk of severe allergic events while taking it.
A 2014 paper described for the first time the H3 reverse agonist/ selective antagonist effects of two antiarrhythmic drugs, amiodarone and lorcainide. This is a very new finding and has not been investigated yet in humans; however, this behavior would explain some of the neurologic effects of these two medications.
Thioperamide has shown promise in research as an H3 and H4 antihistamine, but is not available for patient use.
I have seen blurbs on forums and the internet in which people state that amphetamines are H3 antagonists and doxepin is an H4 antihistamine. I cannot find any evidence that this is the case. Amphetamines interact with the transport of histamine in a very complex way, and that can theoretically interfere with the ability of cells to use histamine. However, this is not the same as a true antihistamine, and the effect of amphetamines on histamine has been difficult to quantify.