Britannica
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Which side effects besides drowsiness can antihistamines cause?
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antihistamine
Antihistamines such as Benadryl (diphenhydramine) and Claritin (loratadine) can be purchased without prescriptions. Both of those agents act by blocking H1 receptors. However, whereas Benadryl binds to those receptors in the central nervous system (CNS), causing drowsiness, Claritin does not readily enter the CNS and thus does not normally cause drowsiness.
While drowsiness is the most frequently reported side effect of antihistamines in adults, these medications can cause several other undesirable reactions depending on the specific drug and the individual patient.
According to the Britannica entry on antihistamines, other potential side effects include:
- Gastrointestinal irritation
- Headache
- Blurred vision
- Dryness of the mouth
It is important to note that the incidence and severity of these effects vary by person and medication. Additionally, older H1 antihistamines may impair performanceāsuch as when drivingāand can enhance the effects of alcohol or other central nervous system depressants. Newer H1 antihistamines are generally designed to avoid the sedative effects associated with earlier versions because they do not cross the blood-brain barrier as readily.1