Loratadine
H1 antihistamine · also known as Claritin, loratadine
Second-generation H1 antihistamine sold without a prescription; metabolised to desloratadine.
- How it relates to mast cells
- Acts after mast-cell mediators are released
- Types of studies cited
- Randomised controlled trial
- Approved in the US for
- hay fever and upper respiratory allergy symptoms
- Known for
- Sold as non-drowsy. Its label warns about drowsiness only for taking more than directed, rather than carrying the plain drowsiness-may-occur warning that cetirizine and levocetirizine both have. Source
- Availability
- sold over the counter in the US, without a prescription
What this relationship means: Acts after mast-cell mediators are released rather than stabilising the mast cell itself. This includes treatments that block mediator receptors, degrade a mediator, or oppose the physiology of an acute reaction. It describes where the intervention acts, not its clinical importance.
Mechanism of action
Mechanism of action
Loratadine is a second-generation H1 receptor antagonist. It blocks the H1 receptor after mast-cell mediators have been released, and penetrates the central nervous system less than first-generation agents.
It is metabolised to desloratadine, which is separately marketed and has its own entry. That relationship is why the two behave similarly, and why a reader who has tried one may find the other described in the same terms.
Sources
- Loratadine US over-the-counter Drug Facts label Drug label · link checked 25 Aug 2026
- Cetirizine versus hydroxyzine and placebo in chronic idiopathic urticaria Peer-reviewed study 1996 PMID 8893110 · link checked 21 Aug 2026
- Mast Cell Activation Syndrome and Mastocytosis: Initial Treatment Options and Long-Term Management Review article 2019 PMID 30961835 · link checked 20 Aug 2026