Chlorcyclizine is a first generation phenylpiperazine class antihistamine used to treat urticaria, rhinitis, pruritus, and other allergy symptoms. Chlorcyclizine also has some local anesthetic, anticholinergic, and antiserotonergic properties, and can be used as an antiemetic. Chlorcyclizine temporarily relieves the symptoms due to hay fever or other upper respiratory allergies. It has also being shown to possess in vitro and in vivo activity against hepatitis C virus.

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.

Carabestine is the active first-pass metabolite of Ebastine and acts as a histamine H1 receptor antagonist which has been investigated as a potential allergy medication. Ebastine is marketed under a number of brand names.

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.

Etiprednol dicloacetate (BNP-166; ethyl-17alpha-dichloroacetoxy-11beta-hydroxyandrosta-1,4-diene-3-one-17beta-carboxylate) is a new soft steroid. The compound proved to be a dissociated glucocorticoid, showing a reduction in transactivating activity while preserving transrepressive abilities. The compound effectively decreased cytokine production in lipopolysaccharide-stimulated lymphocytes and attenuated lectin-induced proliferation of blood mononuclear cells in tissue culture. The significant local effect of the compound will very likely be accompanied by a drastically reduced systemic activity indicating an encouraging selectivity of the pharmacological action of etiprednol dicloacetate. Etiprednol dicloacetate had been in a clinical trial for the treatment of allergic rhinitis, asthma and Crohn's disease. However, development has been discontinued.

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.

Chelidonic acid (CA) is a γ-pyrone which is contained in the rhizome of Chelidonium majus L. It has multiple pharmacological effects including those of a mild analgesic, an antimicrobial, an oncostatic, a central nervous system sedative and the anti-inflammatory effect. Chelidonic acid evokes antidepressant-like effect through the up-regulation of BDNF in forced swimming test. Chelidonic acid administration significantly increased the mRNA expression of hippocampal estrogen receptor-β. The levels of hippocampal interleukin (IL)-1β, IL-6, and tumor necrosis factor-α were effectively attenuated by the administration of chelidonic acid. In addition, chelidonic acid significantly increased the levels of 5-hydroxytryptamine (serotonin), dopamine, and norepinephrine compared with those levels for the mice that were administered distilled water in the hippocampus. Chelidonic acid might serve as a new therapeutic strategy for the regulation of depression associated with inflammation.

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.