Many are ingredients of compound preparations used to treat coughs or the common cold.Patients for whom an antihistamine has been prescribed should be instructed about the side effects of these drugs, including drowsiness, dizziness, and muscular weakness.These side effects present a special hazard in driving an automobile or operating heavy machinery.

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Agents blocking H2 receptors, used to inhibit gastric secretion in peptic ulcer, are usually called substance capable of reducing the physiological and pharmacological effects of histamine, including a wide variety of drugs that block histamine receptors.

Many such drugs are readily available as over-the-counter medicines for the management of allergies.

Toxicity resulting from the overuse of antihistamines and their accidental ingestion by children is common and sometimes fatal.

These substances do not completely stop the release of histamine, and the ways in which they act on the central nervous system are not completely understood.

The antihistamines are divided into histamine-blocking drugs are effective in the control of gastric secretions and are often used in the treatment of gastroesophageal reflux.

Antihistamines can both stimulate and depress the central nervous system. One of a group of drugs which act against histamine-a powerful and highly irritant agent released in the body by MAST CELLS, after contact with certain ALLERGENS.

Antihistamine drugs fall into two groups-those that block H receptor blockers include diphenhydramine, chlorpheniramine (chlorphenamine) (Piriton), terfenadine (Triludan), promethazine (Phenergan), cyproheptadine (Periactin), mequitazine (Primalan) and phenindamine (Thephorin).

HAny substance that reduces the effect of histamine or blocks histamine receptors, usually the histamine 1 (H1) receptor.

It is used in the treatment of allergic conjunctivitis and also in the temporary relief of minor allergic symptoms of the eye.