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.

Phenindamine (thephorin or 2-methyl-9-phenyl-2,3,4,9-tetrahydro-1-pyridindene) a pyridindene derivative proved to be a potent antihistaminic. Phenindamine was used to treat sneezing; runny nose; itching, watery eyes; hives; rashes; itching; and other symptoms of allergies and the common cold.

Diphenhydramine is an antihistamine which is used in the combination with naproxen sodium for the relief of occasional sleeplessness when associated with minor aches and pains. Diphenhydramine has a role nighttime sleep-aid and naproxen sodium is a pain reliever. In addition, diphenhydramine used in relieving symptoms in patients with moderate-to-severe seasonal allergic rhinitis. Diphenhydramine acts as an antagonist of histamine H1 receptor. Besides, was shown potential to repurpose diphenhydramine as an anti-melanoma therapeutic agent, it induces melanoma cell apoptosis by suppressing STAT3/MCL-1 survival signaling pathway.

Acrivastine is a triprolidine analog antihistamine indicated for the treatment of allergies and hay fever. As an H1 receptor antagonist, it functions by blocking the action of histamine at this receptor thereby preventing the symptoms associated with histamine release such as pruritis, vasodilation, hypotension, edema, bronchoconstriction, and tachycardia. Acrivastine is currently available in combination with pseudoephedrine as the FDA-approved product Semprex-D. It’s used for the relief of symptoms associated with seasonal allergic rhinitis such as sneezing, rhinorrhea, pruritus, lacrimation, and nasal congestion. Acrivastine, a structural analog of triprolidine hydrochloride, exhibits H1-antihistaminic activity in isolated tissues, animals, and humans, and has sedative effects in humans. The propionic acid derivative of acrivastine is a metabolite in several animal species (as well as in man) and also exhibits H1-antihistaminic activity.

Astemizole is antihistamine drug, discovered by Janssen Pharmaceutical and used to prevent sneezing, runny nose, itching and watering of the eyes, and other allergic symptoms. The drug was withdrawn from U.S. market in 1999 due to the potential to cause arrhythmias at high doses.

Terfenadine under brand name Seldane was used for the treatment of allergic rhinitis and allergic skin disorders but was withdrawn because of the serious side effect, heart rhythm problems. Terfenadine is a potent antagonist of histamine H1-receptor-mediated responses.

Azatadine is an antihistamine, which blocks the effects of the naturally occurring chemical histamine in the body. Azatadine is used to treat sneezing; runny nose; itching, watery eyes; hives; rashes; and other symptoms of allergies and the common cold. The antihistamines antagonize those pharmacological effects of histamine, which are mediated through activation of H1- receptor sites and thereby reduce the intensity of allergic reactions and tissue injury response involving histamine release.

Thiethylperazine is a antiemetic, which was used for the treatment of nausea and vomiting in patients undergoing radiotherapy, chemotherapy or as a postoperative care. Thiethylperazine exerts its therapeutic effect by blocking dopamine receptors in brain. The drug is capable of potentiating CNS depressants as well as atropine.

Methdilazine is a phenothiazine compound with antihistaminic activity. Methdilazine binds to the histamine H1 receptor. This blocks the action of endogenous histamine, which subsequently leads to temporary relief of the negative symptoms brought on by histamine. It is used for the symptomatic relief of hypersensitivity reactions and particularly for the control of pruritic skin disorders.