Types of antihistamine and their effects
Antihistamine medicines are classified in three groups. These are:
first-generation antihistamines – which cause drowsiness in most people and include diphenhydramine and chlorphenamine
second- or third-generation antihistamines – which are less likely to cause drowsiness and include loratadine and cetirizine
Second- or third-generation antihistamines are usually recommended. Don't underestimate the levels of drowsiness caused by first-generation antihistamines – their effects can continue into the next day if you take them at night.
An exception to this is sometimes made if the drowsiness caused by first-generation antihistamines can be beneficial, for example in cases where itchy skin may be causing sleep problems.
Read more about the side effects of antihistamines.