Key Takeaways: Cetirizine Side Effects

Most common: Fatigue, drowsiness, dry mouth, headache, and nausea. These are usually mild and transient.
Onset: Side effects typically begin within a few hours of taking the first dose.
Duration: Mild effects often resolve within hours to days as your body adjusts. If they persist, consult a doctor.
Contraindications: Severe kidney disease, known allergy to cetirizine or related drugs, and children under 6 years (tablets).
Interactions: Avoid alcohol; no significant food interaction.

Cetirizine is generally well tolerated, but like all medicines it can cause side effects. Understanding what to expect and when helps you use it safely. Below we detail the side effect profile based on the official Patient Information Leaflet.

Important Medical Advice

Seek immediate medical help if: you develop signs of a severe allergic reaction (rash, itching, swelling of face/lips/tongue, difficulty breathing), or if you have thoughts of self‑harm. Overdose may cause confusion, dilated pupils, fast heartbeat, and urinary retention – contact your doctor straight away.

What Are the Common Side Effects of Cetirizine?

Based on clinical trials and post‑marketing experience, the following side effects are reported with cetirizine. Frequencies are defined as: common (≥1/100 to <1/10), uncommon (≥1/1,000 to <1/100), rare (≥1/10,000 to <1/1,000), very rare (<1/10,000), and not known (cannot be estimated).

Common (may affect up to 1 in 10 people)

Fatigue
Somnolence (sleepiness)
Dizziness
Headache
Dry mouth
Nausea (feeling sick)
Diarrhoea (in children only)
Pharyngitis (sore throat – children only)
Rhinitis (swelling and irritation inside the nose – children only)

Uncommon (may affect up to 1 in 100 people)

Pruritus (itching)
Rash
Abdominal pain
Agitation
Asthenia (feeling of weakness)
Malaise (feeling generally unwell)
Paraesthesia (abnormal skin sensations, tingling)

When Do Cetirizine Side Effects Start?

Most side effects appear shortly after starting treatment, often within the first few doses. Because cetirizine is rapidly absorbed (peak plasma levels at 1‑2 hours), effects like drowsiness or dry mouth can begin within the first hour and may be most noticeable during the first few days. If you experience any unusual symptoms, note when they started and discuss with your pharmacist or doctor.

Serious allergic reactions, though very rare, typically occur soon after taking the medicine but can also develop later. Always be alert for symptoms like swelling or difficulty breathing.

How Long Do Cetirizine Side Effects Last? (Side Effects Timeline)

The duration of side effects varies depending on the individual and the specific effect. Here’s a general timeline:

Mild effects (drowsiness, dry mouth): Often improve within a few hours to days as your body adjusts. If you take cetirizine regularly, these may diminish after the first week.
Gastrointestinal effects (nausea, diarrhoea): Usually resolve within a day or two. Staying hydrated helps.
Skin reactions (rash, itching): If mild, they may fade within days. Persistent or worsening rash should be evaluated by a doctor.
Rare effects (e.g., liver problems, severe skin reactions): These require immediate medical attention and may last until the condition is treated.

Remember, the elimination half‑life of cetirizine is 8‑11 hours, so the drug is mostly cleared within 2‑3 days. Side effects directly related to the drug usually resolve as the drug leaves your system.

Cetirizine Contraindications: Who Should Not Take Cetirizine?

Do not take cetirizine if:

You have severe kidney disease (creatinine clearance below 10 ml/min).
You are allergic to cetirizine, hydroxyzine, or any piperazine derivatives, or to any of the tablet ingredients (lactose, etc.).
You are under 6 years of age (for the tablet form; liquid may be used for younger children under medical supervision).

Warnings and precautions: Consult your doctor before use if you have kidney problems (dose adjustment may be needed), epilepsy or risk of seizures, or factors predisposing to urinary retention (e.g., spinal cord injury, enlarged prostate).

Food and Alcohol Interactions with Cetirizine

Food: Cetirizine can be taken with or without food. Food does not reduce the amount absorbed; it may slightly delay absorption but this has no clinical impact.

Alcohol: Although no direct interaction has been observed at recommended doses (up to 0.5 g/L blood alcohol), it is advisable to avoid or limit alcohol while taking cetirizine. Alcohol may increase the risk of drowsiness and impaired concentration, especially in sensitive individuals.

Rare and Serious Side Effects

Although uncommon, the following serious side effects have been reported. Stop taking cetirizine and contact your doctor immediately if you experience any of these:

Rare (may affect up to 1 in 1,000 people)

Tachycardia (fast heartbeat)
Oedema (generalised swelling due to fluid retention)
Liver function abnormal
Convulsions
Weight increased
Aggression, confusion, depression, hallucination, insomnia
Urticaria (swelling, redness, itchiness of skin)

Very rare (may affect up to 1 in 10,000 people)

Thrombocytopenia (low platelets – increased bleeding/bruising)
Accommodation disorder (impaired focusing), blurred vision, oculogyration (uncontrolled eye movement)
Syncope (fainting), dyskinesia (involuntary movements), dystonia (abnormal muscle contractions), tremor, dysgeusia (altered taste)
Tics (sudden repetitive movements)
Fixed drug eruption (round/oval red patches)
Abnormal urine elimination (bed‑wetting, pain/difficulty passing urine)

Not known (cannot be estimated from available data)

Increased appetite
Suicidal ideation (thoughts of self‑harm)
Nightmare
Amnesia, memory impairment
Vertigo
Urinary retention (inability to empty bladder)
Intense itching and/or urticaria upon stopping treatment
Joint pain
Rash with blisters containing pus
Hepatitis (inflammation of the liver)

If you notice any side effect not listed, please inform your doctor or pharmacist. You can also report side effects directly via the Yellow Card Scheme at www.mhra.gov.uk/yellowcard.

Cetirizine Side Effects FAQs

Does cetirizine cause weight gain?

Weight gain is a rare side effect (may affect up to 1 in 1,000 people). If you notice unexplained weight increase, consult your doctor.

Can cetirizine make you feel anxious or agitated?

Agitation is an uncommon side effect. If you experience unusual anxiety or agitation, speak to your doctor.

How long does drowsiness from cetirizine last?

Drowsiness usually occurs within the first few hours and may improve after a few days of regular use. If it persists, try taking the dose in the evening.

Can I take cetirizine if I have high blood pressure?

Cetirizine is generally safe for people with high blood pressure, as it does not affect blood pressure. However, always check with your doctor or pharmacist.

What should I do if I experience severe side effects?

Stop taking cetirizine and seek medical attention immediately if you have difficulty breathing, swelling, thoughts of self‑harm, or signs of a severe skin reaction.