Antihistamines are drugs that fight the effects of allergies. When a person experiences allergic symptoms such as congestion, sneezing, itching or runny nose, a chemical called histamine is responsible for this allergic reaction. Taking an antihistamine can block the action of histamine and reduce allergic symptoms.
Most of the time, antihistamines are most effective when taken before allergic symptoms occur, though they can also provide relief after the symptoms have begun. In some cases, antihistamines are combined with decongestants and pain relievers to treat the symptoms of a cold.
Types of Antihistamines
Antihistamines are often described as being “first-generation” or “second-generation” antihistamines. The first-generation antihistamines are effective at stopping allergy symptoms, but the drawback to these drugs is that they typically cause drowsiness. However, in some cases this side effect is an advantage, which is why these antihistamines are frequently incorporated into cold remedies to be taken before bedtime or in drugs for insomnia, for example.
Second-generation antihistamines, which were developed more recently, include fexofenadine, cetirizine and loratadine. For the most part, these drugs are free of side effects and do not cause drowsiness.
Though these drugs are generally considered safe, it’s important to take some precautions with antihistamines. For example, driving or operating machinery is generally not recommended when taking first-generation antihistamines. And with all antihistamines, it’s possible to take too much, so check the label to make sure not to take more than one medication containing antihistamine. People with certain health problems -- such as glaucoma, thyroid disease, enlarged prostate, breathing problems, high blood pressure or heart disease -- need to be careful about first-generation antihistamines. Kidney or liver problems can pose some risks for those taking second-generation antihistamines. It’s best to speak with a doctor in these situations.
SOURCES: American Academy of Otolaryngology – Head and Neck Surgery; American Academy of Family Physicians.