Brand name versus active ingredient
A brand name is a trademark owned by a company. The generic name identifies the active ingredient and is the same worldwide. Zyrtec is a brand; cetirizine is the drug.
This distinction is not pedantry. It has three practical consequences.
Store brands are the same drug. A supermarket own-brand cetirizine must meet the same standards for the active ingredient as the branded version. Inactive ingredients and appearance may differ; the active ingredient does not. The price difference frequently does not reflect any difference in the medicine.
Brand names cover multiple products. Companies extend a familiar brand across a product line. Some of those products contain a different or additional active ingredient — most commonly a decongestant, indicated by a "-D" suffix. Buying by brand name alone does not tell you what is in the box.
Formulations change. A product you bought last year under the same name may not have the same recipe today. Manufacturers reformulate, and the front of the package is not where they announce it.
The comparison underneath
Once you strip away the branding, this is the hydroxyzine versus cetirizine comparison: a first-generation prescription antihistamine against a second-generation over-the-counter one.
Cetirizine is chemically derived from hydroxyzine, modified so that it crosses into the brain far less. That is why it causes much less sedation and can be used during a working day, and it is why hydroxyzine — which crosses readily — is prominently sedating.
Their labeled uses also differ: hydroxyzine's labeling covers symptomatic relief of anxiety and tension, which cetirizine's does not. The full ingredient-level comparison is here.
The combination-product trap
The most common mistake in the allergy aisle is buying a combination product without registering what has been added.
A "-D" suffix generally indicates an added decongestant such as pseudoephedrine. Decongestants have their own considerations, particularly for people with high blood pressure, heart conditions, or certain other health issues, and they can also affect sleep.
Products aimed at night-time symptoms may contain a sedating first-generation antihistamine instead of, or in addition to, a second-generation one. Multi-symptom cold products often bundle a pain reliever, a cough suppressant, a decongestant and an antihistamine into a single dose.
Each of those ingredients can duplicate something you already take. The check is always the same: read the active ingredients panel, count how many things are in there, and ask a pharmacist if anything looks like it overlaps with a prescription.
Making the pharmacy counter work for you
Pharmacists are licensed medication experts, available without an appointment, and in most community pharmacies they will answer questions at no charge. The over-the-counter aisle is precisely where that expertise is most underused, because people assume no advice is needed for something sold off a shelf.
Useful things to bring: your current medicine list, the product you are considering, and a clear statement of the symptom you are trying to address. Useful things to ask: does this duplicate anything I take, is the store brand equivalent, and is there a reason to prefer one formulation over another for my situation.
Daytime allergy goals versus sedating antihistamines
Cetirizine (Zyrtec) is often chosen when people want allergy relief with less sedation than older antihistamines, while hydroxyzine is more strongly associated with drowsiness in labeling. Ask whether your primary problem is daytime allergy symptoms, itch that disrupts sleep, or anxiety-related use described on a hydroxyzine label. Ask what to do if daytime sleepiness interferes with work or school. Do not combine sedating antihistamines without professional guidance.