How long does it take for Loratadine to work?

Claritin is an antihistamine that take a bit longer to build up in your system as opposed to the older antihistamines like Benadryl. The plus side is there is minimal drowsiness. For a drug to reach 90% of it's steady state levels after constant usage, it takes about 3.3 half lives, so it takes about a day for Claritin (8hr half life) to get to it's maximal effectiveness. It doesn't cause drowsiness because it doesn't cross the blood-brain barrier like earlier antihistamines, such as Benadryl.