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 drowsiness.

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.