Zyrtec Generic (Cetirizine 5mg/10mg)

Medically reviewed by Dr. Sarah Mitchell, RPh, Clinical Pharmacist — Updated January 2026

What Is Cetirizine (Zyrtec/Reactine)? — Mechanism of Action

Cetirizine hydrochloride is a second-generation selective peripheral H1 receptor antagonist — it works by competitively and selectively blocking the histamine H1 receptor, preventing histamine from binding and triggering the allergic cascade that produces allergy symptoms.

The allergy cascade cetirizine interrupts: When a sensitised individual is exposed to an allergen (pollen, pet dander, dust mite allergen, ragweed), mast cells and basophils in the nasal mucosa, conjunctiva, and skin rapidly degranulate — releasing large quantities of histamine. Histamine then binds to H1 receptors on local tissues, producing the characteristic allergic response: vasodilation and plasma extravasation causing nasal congestion, glandular hypersecretion causing rhinorrhea (runny nose) and watery eyes, sensory nerve stimulation causing sneezing and itch, and smooth muscle contraction contributing to bronchospasm in allergic asthma.

Why cetirizine is "second-generation" — the key pharmacological properties: First-generation antihistamines (diphenhydramine/Benadryl, chlorpheniramine) readily cross the blood-brain barrier due to their high lipophilicity and neutral charge. CNS penetration produces significant sedation, impaired cognition, anticholinergic effects (dry mouth, urinary retention, constipation), and significant next-day cognitive impairment even when sedation has apparently worn off. Cetirizine overcomes these limitations through:

• Low lipophilicity: Cetirizine is a zwitterionic molecule (has both positive and negative charges at physiological pH) with low lipid solubility — reducing passive diffusion across the blood-brain barrier compared to first-generation antihistamines
• P-glycoprotein (P-gp) efflux pump substrate: Cetirizine is a substrate for P-glycoprotein, an efflux transporter at the blood-brain barrier that actively pumps cetirizine back out of the CNS — further reducing CNS penetration. This P-gp-mediated efflux is a key mechanism explaining cetirizine's low sedation profile
• High peripheral H1 receptor binding selectivity: Cetirizine binds H1 receptors in peripheral tissues (nasal mucosa, skin, conjunctiva) with high affinity while maintaining low CNS H1 occupancy — producing effective peripheral antihistamine activity with minimal central sedation
• Metabolic stability: Unlike many antihistamines, cetirizine undergoes minimal hepatic metabolism — it is excreted largely unchanged in urine. This reduces the formation of active metabolites that might have different CNS penetration profiles and makes dosing more predictable

Health Canada-Approved Indications

1. Seasonal Allergic Rhinitis (Hay Fever) — the primary Canadian indication: Hay fever affects approximately 25 to 30% of Canadians — one of the most prevalent chronic conditions in Canadian healthcare. Cetirizine effectively relieves the major symptoms of seasonal allergic rhinitis: sneezing, rhinorrhea (runny nose), nasal pruritus (itching), and nasal congestion. It also addresses ocular symptoms (itchy, watery, red eyes) that commonly accompany hay fever. The three major seasonal allergy periods in Canada where cetirizine is most heavily used:

• Birch pollen season (April–May across Ontario, Quebec, Maritimes): Birch is the most potent tree allergen in Canada — cetirizine is commonly started 1 to 2 weeks before the expected pollen season start date to establish steady-state H1 receptor occupancy before allergen exposure begins
• Grass pollen season (June–August across the Prairies and southern Ontario/Quebec): Timothy grass, bluegrass, and ryegrass are the dominant grass allergens in Canada. This is typically the longest and most widespread allergy season
• Ragweed season (mid-August to first frost — Ontario, Quebec, Maritimes): Ragweed (Ambrosia artemisiifolia) is the most impactful seasonal allergen in Canada — affecting approximately 1 in 6 Canadians. The Windsor-Sarnia corridor has the highest ragweed concentrations in North America, with Toronto, Hamilton, Montreal, and Ottawa also severely affected. Many Canadian physicians recommend starting cetirizine in early August, before ragweed season begins, and continuing through October

2. Perennial Allergic Rhinitis (Year-Round Allergy) — the chronic use indication: Many Canadians have year-round allergic rhinitis driven by indoor perennial allergens rather than seasonal pollens. The major perennial allergens in Canadian homes include house dust mites (thriving in the warm, sealed Canadian indoor environment during winter), cat and dog dander (approximately 57% of Canadian households have pets), and mould spores. For these patients, cetirizine is often taken continuously year-round — its safety profile supports long-term daily use. Consistent daily dosing maintains steady-state H1 blockade more effectively than as-needed dosing for perennial allergy management.

3. Chronic Spontaneous Urticaria (CSU/Chronic Hives) — second-line indication in Canada: Cetirizine is a first-line pharmacotherapy for chronic spontaneous urticaria — itchy wheals (hives) that persist for more than 6 weeks without an identifiable external trigger. CSU affects approximately 1% of Canadians. The standard Canadian approach per the Canadian Dermatology Association (CDA) and international urticaria guidelines: cetirizine 10mg once daily is the starting dose; if inadequate response, the dose can be increased up to 20–40mg daily (off-label dose escalation, specialist supervision recommended) before adding second-line agents (omalizumab/Xolair).

4. Allergic Conjunctivitis: Red, itchy, watery eyes from allergen exposure — cetirizine's systemic H1 blockade reduces ocular symptoms as part of the overall allergic rhinoconjunctivitis picture.

5. Atopic Dermatitis (Eczema) — adjunct use: Cetirizine is used as adjunctive therapy to reduce pruritus (itch) in atopic dermatitis, though it is not a primary eczema treatment and has limited evidence for modifying the underlying condition.

Cetirizine vs Loratadine vs Fexofenadine — The Canadian Antihistamine Comparison

The most common question Canadian allergy patients and pharmacists face is choosing between the three major second-generation antihistamines available OTC in Canada. This is the most-searched comparison for cetirizine in Canada:

The practical Canadian guidance: Choose cetirizine (Zyrtec/Reactine) if you have severe allergy symptoms, chronic urticaria, or find loratadine or fexofenadine insufficient — and take it in the evening to use the mild sedative effect to your advantage (helps sleep during ragweed season when allergy symptoms also disrupt sleep). Choose loratadine or fexofenadine if you need maximum daytime alertness (shift workers, drivers, precision tasks), cannot tolerate even mild sedation, or have previously found cetirizine excessively sedating.

Cetirizine vs Levocetirizine (Xyzal) — The Active Metabolite Question

A frequently asked question in Canadian pharmacies is whether levocetirizine (Xyzal — available in Canada on prescription) is better than cetirizine. The answer requires understanding the relationship between the two molecules:

• Levocetirizine is the R-enantiomer of cetirizine — cetirizine is a racemic mixture of R- and S-enantiomers. The R-enantiomer (levocetirizine) has approximately twice the H1 receptor binding affinity of racemic cetirizine
• Dose equivalence: Levocetirizine 5mg is considered approximately equivalent in antihistamine effect to cetirizine 10mg — you get the same H1 blockade from half the molecule at half the dose
• Sedation: Levocetirizine 5mg may produce marginally less sedation than cetirizine 10mg in some patients, though clinical differences are modest
• Canadian availability: Levocetirizine requires a prescription in Canada — cetirizine is available OTC. For most Canadian patients with typical allergy symptoms, cetirizine 10mg provides fully adequate and equivalent antihistamine benefit at a much lower cost without requiring a physician visit
• Clinical recommendation: There is no compelling clinical evidence that levocetirizine provides meaningfully superior allergy symptom control compared to cetirizine for the majority of Canadian patients. Cetirizine remains the first-choice antihistamine for most Canadians based on efficacy, cost, and OTC accessibility

Dosing in Canada — Complete Guide

Adults and adolescents 12 years and older:

• Standard dose: 10mg once daily
• Timing: Evening is preferred for most Canadians — cetirizine's mild sedative effect in susceptible individuals is used advantageously at night. Morning dosing is acceptable if evening dosing causes next-day grogginess
• Consistent daily dosing for seasonal allergy: Start 1 to 2 weeks before the expected allergy season onset and continue throughout the season for maximum benefit. This pre-seasonal approach establishes steady-state H1 occupancy before allergen exposure begins
• Year-round dosing for perennial allergy: Daily year-round dosing is appropriate and safe for patients with perennial allergic rhinitis or chronic urticaria

Children 6 to 11 years:

• 5mg or 10mg once daily depending on symptom severity
• 5mg is the standard starting dose for most children in this age group

Children 2 to 5 years:

• 2.5mg once daily (using liquid cetirizine formulation)
• May be increased to 5mg once daily or 2.5mg twice daily based on physician guidance

Renal impairment — dose reduction required: Cetirizine is primarily excreted unchanged by the kidneys — dose adjustment is required for Canadian patients with significant renal impairment:

• Moderate renal impairment (CrCl 11–31 mL/min): 5mg once daily
• Severe renal impairment requiring dialysis: 5mg once daily
• End-stage renal disease on haemodialysis: Contraindicated (cetirizine is not effectively removed by dialysis)

Hepatic impairment: Dose adjustment is generally not required for mild to moderate hepatic impairment since cetirizine undergoes minimal hepatic metabolism. Caution is advised in severe hepatic failure.

Taking cetirizine: Swallow the tablet whole with a glass of water. Can be taken with or without food — food does not significantly affect absorption. Consistency is more important than timing with food.

Side Effects — Complete Canadian Guide

Very common or common (affecting >1% of patients):

• Drowsiness/somnolence: The most discussed cetirizine side effect — occurring in approximately 10 to 15% of users, making it slightly more sedating than loratadine or fexofenadine but substantially less sedating than first-generation antihistamines. The degree of sedation is highly individual — some Canadians find cetirizine completely non-sedating while others find it causes noticeable grogginess. Key management strategies: (1) take in the evening so any sedative effect occurs during sleep; (2) avoid alcohol while taking cetirizine — even small amounts significantly potentiate the sedative effect; (3) assess individual response before driving or operating machinery; (4) if persistent daytime drowsiness is problematic, consider switching to loratadine or fexofenadine
• Dry mouth: Due to mild anticholinergic effects — substantially less than first-generation antihistamines. Stay well hydrated; sugar-free gum or lozenges help
• Headache: Mild, transient — usually resolves with continued use
• Fatigue: Related to the mild sedative effect — morning fatigue if taken at night, or daytime fatigue if taken in the morning in susceptible individuals
• Nausea and abdominal discomfort: Mild GI side effects in a small proportion of patients — taking with food reduces
• Dizziness: Uncommon — avoid driving until individual response is assessed

Important — alcohol interaction: Alcohol has an additive CNS depressant effect with cetirizine. Even one or two drinks while taking cetirizine can produce significant sedation, impaired coordination, and slowed reaction time in patients who otherwise experience no drowsiness from cetirizine alone. Canadian patients taking cetirizine should avoid alcohol or limit intake substantially, particularly before driving or operating machinery.

Rare but reportable side effects:

• Paradoxical CNS stimulation (excitability, agitation, insomnia) — occurs rarely, more common in children
• Allergic reactions to cetirizine itself — rash, urticaria, angioedema, anaphylaxis are possible (rare). Stop immediately and seek medical attention if signs of allergic reaction develop. Cetirizine is contraindicated in patients with known hypersensitivity to cetirizine, hydroxyzine (a structurally related antihistamine), or any excipient
• Urinary retention — rare; more relevant in patients with pre-existing lower urinary tract issues (e.g., elderly men with benign prostatic hyperplasia)
• Liver function abnormalities — very rare; reported in post-marketing surveillance

Pregnancy and Breastfeeding

Pregnancy: Cetirizine is classified as Pregnancy Category B in Canada — animal studies have not demonstrated teratogenic risk, and while adequate well-controlled human pregnancy studies are lacking (as with essentially all medications), cetirizine is generally considered one of the preferred antihistamine choices during pregnancy when antihistamine therapy is required. Many Canadian obstetricians and family physicians consider cetirizine an acceptable option in the second and third trimesters. The first trimester is a period of heightened caution for all medications — discuss with your Canadian obstetrician before starting or continuing cetirizine during the first trimester. Loratadine is often cited alongside cetirizine as a preferred antihistamine in pregnancy in Canadian guidelines.

Breastfeeding: Cetirizine is excreted in breast milk in small amounts. Health Canada advises caution — if antihistamine therapy is required during breastfeeding, loratadine is generally preferred due to its lower potential for sedation in the nursing infant. Consult your physician or pharmacist if you are breastfeeding and need antihistamine therapy.

Who Should Not Take Cetirizine

• Known hypersensitivity to cetirizine, hydroxyzine, or any tablet excipient
• End-stage renal disease on dialysis — cetirizine accumulates
• Use with caution: moderate to severe renal impairment (reduce dose — see dosing section); epilepsy (antihistamines may lower seizure threshold); pre-existing urinary retention disorders; severe hepatic impairment
• Children under 2 years: not recommended without specialist supervision

Cetirizine in Canada — OTC Status and Reactine

In Canada, cetirizine is classified as a non-prescription (OTC) medication — available without a prescription at all major Canadian pharmacy chains and grocery stores with pharmacy departments including Shoppers Drug Mart, Rexall, Pharmasave, Costco Pharmacy, Walmart Pharmacy, and most independent pharmacies.

The dominant Canadian brand name for cetirizine is Reactine (Johnson & Johnson Consumer Inc.) — when Canadians refer to "Reactine," they are referring to cetirizine. Zyrtec is the international brand name for the same molecule. Generic cetirizine (Zyrtec Generic at drugs-canada.com) contains the identical active ingredient as Reactine and Zyrtec at the same doses, at substantially lower cost.

Despite OTC availability in Canada, cetirizine is a pharmacologically active medication — it has clinically significant drug interactions (particularly with alcohol and CNS depressants), requires dose adjustment in renal impairment, and should be used with caution in pregnant or breastfeeding patients. OTC accessibility does not mean cetirizine is without clinical considerations.

Delivery to All Canadian Provinces and Territories

drugs-canada.com ships Zyrtec Generic discreetly to all Canadian provinces and territories. Standard delivery: 4–9 business days.

Ontario (Toronto, Ottawa, Hamilton, London, Brampton, Mississauga, Kitchener-Waterloo) — Quebec (Montreal, Quebec City, Laval, Gatineau, Sherbrooke) — British Columbia (Vancouver, Surrey, Burnaby, Victoria, Kelowna, Abbotsford) — Alberta (Calgary, Edmonton, Red Deer, Lethbridge) — Manitoba (Winnipeg, Brandon) — Saskatchewan (Saskatoon, Regina) — Nova Scotia (Halifax, Sydney) — New Brunswick (Moncton, Saint John, Fredericton) — Newfoundland and Labrador (St. John's, Corner Brook) — Prince Edward Island (Charlottetown) — Northwest Territories (Yellowknife) — Yukon (Whitehorse) — Nunavut (Iqaluit).

All orders are dispatched in plain, unmarked packaging with no reference to the contents or sender. Every order includes a tracking number.

Frequently Asked Questions — Cetirizine (Zyrtec/Reactine) in Canada

Is Zyrtec the same as Reactine in Canada? Yes — Reactine is the dominant brand name for cetirizine in Canada (marketed by Johnson & Johnson Consumer). Zyrtec is the same molecule sold under a different brand name internationally. Zyrtec Generic contains identical cetirizine hydrochloride at the same 5mg and 10mg doses as Reactine — the only differences are packaging, brand name, and price. Generic cetirizine is bioequivalent to Reactine and Zyrtec brand products.

Is Zyrtec (cetirizine) non-drowsy in Canada? Cetirizine is classified as a "low-sedating" antihistamine — significantly less sedating than first-generation antihistamines like diphenhydramine (Benadryl). However, it is not entirely free of sedation potential. Approximately 10 to 15% of users experience some degree of drowsiness — more than with loratadine (Claritin) or fexofenadine (Allegra). Taking cetirizine in the evening minimises daytime sedation for most users. Canadians who drive commercially, operate heavy machinery, or require complete alertness during the day may prefer loratadine or fexofenadine. Individual responses vary considerably.

When should I start taking cetirizine for ragweed season in Canada? For optimal allergy control during ragweed season (typically mid-August to first frost in Ontario, Quebec, and the Maritimes), most Canadian allergists and pharmacists recommend starting cetirizine 1 to 2 weeks before the expected season onset — this allows steady-state H1 receptor occupancy to be established before significant allergen exposure begins. Ragweed season in Windsor-Sarnia typically begins around August 1–10; in Toronto and Montreal around August 15–20. A useful resource for monitoring Canadian pollen counts is the Weather Network pollen forecast.

Can I take cetirizine every day for a long time? Yes — cetirizine has an established safety profile for long-term daily use. Many Canadians with perennial allergic rhinitis or chronic urticaria take cetirizine daily year-round for years without significant safety concerns. There is no evidence of tachyphylaxis (loss of effectiveness) with continuous cetirizine use — a common concern that is not supported by clinical evidence. Long-term use does not appear to increase the risk of any serious adverse effect beyond what is seen with short-term use.

How long does delivery to Canada take? Standard delivery to all Canadian provinces and territories takes 4 to 9 business days. All orders arrive in plain, unmarked packaging with no reference to the contents or sender. Every order includes a tracking number.

All information on this page is for general informational purposes only and does not constitute medical advice. While cetirizine is available over-the-counter in Canada, it is a pharmacologically active medication with drug interactions and clinical considerations. Consult a qualified Canadian pharmacist or physician if you have questions about whether cetirizine is appropriate for your specific health situation, particularly if you have kidney disease, are pregnant or breastfeeding, or take other medications including alcohol.