Claritin vs. Zyrtec: Antihistamine Allergy Drug Comparison


What are Claritin and Zyrtec?

Hay fever (allergic rhinitis), hives (urticaria), and pollen-induced asthma
are all reactions to histamines released by the body in response to an allergen
(dust, pollen, or animal dander). Second-generation antihistamine drugs
like Claritin and Zyrtec keep cells from interacting with histamine, thereby
preventing allergy symptoms.

Histamine is a relatively simple, nitrogen-based compound manufactured in
special white blood cells called mast cells. Histamine is a crucial messenger
chemical used for all kinds of important physiological and neurological
functions. The function a histamine molecule performs in any given physiological process depends not on the chemical
itself, but how cell proteins latch onto and interpret it.

Researchers have identified four different histamine receptor proteins thus
far, named H1 through H4. They each kick off drastically different processes
when exposed to histamine. A lot of H1 receptor proteins are located on the
outer membranes of nerve cells and blood vessel cells in the mucous membranes of
the airways and gut – basically any tissue that has exposure to the outside
environment. When, for example, pollen stimulates mast cells to release
histamine, the histamine molecules latch onto the H1 receptor proteins, which
causes capillaries to open, tissue to swell, and membranes to become more
permeable to fluid. In people with allergies, the mast cells overreact to
allergens and release way too much histamine, causing runny nose, itchy eyes,
sneezing, and inflamed airways.

Loratadine and cetirizine are H1 receptor antagonists. This means each
molecule of the medication has a shape and chemical properties that make it fit
into the H1 receptor, locking out the histamine without kicking off the
inflammation reaction.

Older antihistamines like hydroxyzine are blunt instruments compared to
second-generation ones like Claritin and Zyrtec. As mentioned before, histamines
are crucial for all sorts of neurological functions, including maintaining
normal levels of alertness and wakefulness. Older antihistamines helped with
allergy symptoms, but they also blocked H1 receptors in the brain, causing

Molecules of loratadine and cetirizine are shaped in such a way they can’t
fit through the membranes that separate the bloodstream from brain tissue,
meaning Claritin and Zyrtec cause less drowsiness that older antihistamines. According to a 2014 study,
however, second-generation antihistamines — Zyrtec especially — can affect
mood and cause daytime drowsiness more often than doctors initially believed.
So, just because the newer medications are more precise doesn’t mean they’re
without side effects.

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