Antihistamines are a class of agents that block histamine release from histamine-1 receptors and are used to treat the symptoms of an allergic reaction, such as edema (swelling), itch, inflammation (redness), sneezing, or a runny nose or watery eyes.Antihistamines can be further divided into those unlikely to cause drowsiness (non-sedating antihistamines) or those likely to cause drowsiness (sedating antihistamines).As the name suggests, antihistamines block the action of histamine. Never drive or operate machinery when taking one of these drugs and be aware that the effect may persist for some time, or into the next day if you take a dose at night.When someone has an allergy to a normally harmless substance like pollen or pet dander, the immune system treats it as if it were 'foreign' like a virus or bacterium. There is some evidence that people who regularly take sedating antihistamines are more likely to have a serious accident.Antihistamines are primarily used for treating allergic reactions and conditions such as hay fever.Their main side effect is drowsiness, so they can also be used for short-term sleeping problems.The 'Z' drugs were designed to try to overcome some of the problems associated with benzodiazepines, but they act in a very similar way.
Two types of OTC antihistamines are available: first-generation and second-generation. First-generation antihistamines are sometimes used in OTC . Antihistamines prevent histamines from attaching to your cells and causing symptoms.
These are older drugs which are rather non-specific in their action.
Many antihistamines are available over the counter. There are two types of antihistamine – first generation (sedating) and second generation (non-sedating). Antihistamines come in different formulations: tablet, capsule, syrup, nasal spray, gel, cream and lotion.
In fact, most over-the-counter sleep aids contain antihistamines.
These products are intended to be used for only two to three nights at a time, however, such as when stress, travel or other disruptions keep you awake.
Hence they are sometimes also referred to as sedating histamines.