Most people know that there are two types of antihistamines - drowsy and non-drowsy, and there are two types simply due to the advancement in pharmaceuticals.
Drowsy antihistamines are known as first-generation antihistamines, such as chlorphenamine, hydroxyzine, and promethazine.
The non-drowsy antihistamines, which include cetirizine, loratadine, and fexofenadine, are known as second-generation antihistamines.
The only difference between them is the effect of drowsiness, which means that the first-generation antihistamines can also be used as other forms of medical treatment, like insomnia.