Some medications treat multiple conditions and appear multiple times.They are central nervous depressants and interact with brain activity causing its deceleration.They can cross the blood-brain barrier and inhibit one of the other functions of histamines — that is, the pivotal role they play in regulating sleep and wakefulness.This disruption of the action of histamines in the brain results in drowsiness.Allergies occur when your immune system erroneously thinks an innocuous foreign substance, such as pollen or pet dander, is actually dangerous.Histamines jump to action, causing the range of symptoms associated with allergies (sneezing, itchy eyes, chest congestion, wheezing, etc.).At higher doses it may result in slurred speech, staggering gait, poor judgment, and slow, uncertain reflexes.
The list is not exhaustive and not all drugs are used regularly in all countries.
There is some overlap between the terms "sedative" and "hypnotic".
Advances in pharmacology have permitted more specific targeting of receptors, and greater selectivity of agents, which necessitates greater precision when describing these agents and their effects: Doctors often administer sedatives to patients in order to dull the patient's anxiety related to painful or anxiety-provoking procedures.
Antihistamines are typically used to ease allergy symptoms, and work by blocking histamines' attachment to receptors, preventing the compounds from carrying out their functions.
But older, first-generation antihistamines, including diphenhydramine and doxylamine succinate, don't discriminate between which histamine receptors they block.