Pyrilamine (also known as Mepyramine) is a first generation antihistamine, targeting the H1 receptor. However, it rapidly permeates the brain and so often causes drowsiness as a side effect. It is used in over-the-counter combination products for colds and menstrual symptoms. Mepyramine is a histamine H1 receptor inverse agonist. It binds to a G protein-coupled form of the receptor and promotes a G protein-coupled inactive state of the H1 receptor that interferes with the Gq/11-mediated signaling. Mepyramine competes with histamine for binding at H1-receptor sites on the effector cell surface, resulting in suppression of histaminic edema, flare, and pruritus. The sedative properties of Mepyramine occur at the subcortical level of the CNS. It has mild hypnotic properties and some local anesthetic action and is used for allergies (including skin eruptions) both parenterally and locally. It is a common ingredient of cold remedies.

Doxylamine is an antihistamine commonly used as a sleep aid. This drug is also used to relieve symptoms of hay fever (allergic rhinitis), hives (rash or itching), and other allergic reactions. Doxylamine is a member of the ethanolamine class of antihistamines and has anti-allergy power far superior to virtually every other antihistamine on the market, with the exception of diphenhydramine (Benadryl). It is also the most powerful over-the-counter sedative available in the United States, and more sedating than many prescription hypnotics. In a study, it was found to be superior to even the barbiturate, phenobarbital for use as a sedative. Doxylamine is also a potent anticholinergic. Like other antihistamines, doxylamine acts by competitively inhibiting histamine at H1 receptors. It also has substantial sedative and anticholinergic effects. Used alone as a short-term sleep aid, in combination with other drugs as a night-time cold and allergy relief drug. Also used in combination with Vitamin B6 (pyridoxine) to prevent morning sickness in pregnant women.

PF-03654746 is a potent, selective antagonist of the human H3 receptor, developed by Pfizer. It was in the clinical trial phase II for the treatment of excessive daytime sleepiness (EDS) associated with narcolepsy, Tourette syndrome as well as potential anti-allergy applications and in phase I of clinical trial for the treatment of Schizophrenia and Alzheimer's disease, but these investigations were discontinued.

Efletirizine is histamine H1 receptor antagonist. Restricted to topical use. It was under investigation in Phase III (in Europe) clinical studies for the treatment of allergic rhinitis and chronic idiopathic urticarial. Research was discontinued in 2005 due to limited clinical efficacy and safety data. Efletirizine also reduced ocular itching.

Imetit (S-[2-(4-(imidazolyl)ethyl]isothiourea) is a highly specific and potent histamine H3 receptor agonist. It is widely used to study H3-mediated signaling.

Imetit (S-[2-(4-(imidazolyl)ethyl]isothiourea) is a highly specific and potent histamine H3 receptor agonist. It is widely used to study H3-mediated signaling.

Sinomenine is a pure alkaloid extracted from the Chinese medical plant Sinomenium acutum. Caulis Sinomenii is the dried plant stems of Sinomenium acutum and Sinomenium acutum var. cinereum and has been used in Chinese medicine for treating rheumatic diseases for over a thousand years. Sinomenine possesses the anti-arthritic effect, that may be related to the suppression of both Th1 (T-helper 1) and Th2 immune responses, also this potential drug can be used to treat allergic rhinitis, and the mechanism may rely on the improvements of the Th1/Th2 imbalance. In addition, Sinomenine displays antinociceptive activity, possibly through activation of the μ-opioid receptor. Also was discovered, sinomenine significantly improves cardiac function in diabetic rats, which may be attributed to the deactivation of NF-κB and the blockade of inflammatory cytokine-mediated immune reactions.

Sinomenine is a pure alkaloid extracted from the Chinese medical plant Sinomenium acutum. Caulis Sinomenii is the dried plant stems of Sinomenium acutum and Sinomenium acutum var. cinereum and has been used in Chinese medicine for treating rheumatic diseases for over a thousand years. Sinomenine possesses the anti-arthritic effect, that may be related to the suppression of both Th1 (T-helper 1) and Th2 immune responses, also this potential drug can be used to treat allergic rhinitis, and the mechanism may rely on the improvements of the Th1/Th2 imbalance. In addition, Sinomenine displays antinociceptive activity, possibly through activation of the μ-opioid receptor. Also was discovered, sinomenine significantly improves cardiac function in diabetic rats, which may be attributed to the deactivation of NF-κB and the blockade of inflammatory cytokine-mediated immune reactions.

ABT-491 is highly potent, selective and orally active platelet-activating factor (PAF) receptor antagonist, developed by Abbott Laboratories for allergic rhinitis treatment. ABT-491 is a potent antagonist of responses linked to the PAF receptor at the cellular level, especially platelets and neutrophils. ABT-491 was also effective in blocking platelet activation in blood, indicating that the presence of high concentrations of protein and other serum factors slightly alters the ability of ABT-491 to interact with PAF receptor. ABT-491 effectively antagonizes PAF-induced platelet and neutrophil responses at submicromolar concentrations in vitro and exhibits in vivo efficacy in alleviating PAF-mediated inflammatory and pathological processes in various animals, including guinea pigs, mice, and rats, via either i.v., i.p. or p.o. routes.

Pemirolast is a mast cell stabilizer that acts as an antiallergic agent, it is approved in Japan for the treatment of bronchial asthma and of allergic rhinitis. Pemirolast strongly inhibits extracellular Ca2+ influx and the release of intracellular Ca2+, an important factor in the release of chemical mediators, by inhibiting inositol-phospholipid metabolism in mast cells. It also inhibits the release of arachidonic acid. Furthermore contribution of increasing effect on c-AMP based on inhibiting phosphodiesterase is suggested. Main pharmacological effects is an inhibition of release of chemical mediators, e.g. histamine, LTB4, LTC4, LTD4, PGD2, TXB2 and PAF from human lung tissues, abraded fragments of the nasal mucosa, and peripheral leukocytes, rat peritoneal exudate cells, and rat and guniea pig lung tissues.