Does levocetirizine cause diarrhea? A Pharmacological Examination

October 8, 2025 •

3 min read

In clinical trials with children aged 1 to 5 years, diarrhea was reported in 4% of those taking levocetirizine [1.2.1, 1.2.2]. This raises the question for many users: Does levocetirizine cause diarrhea? This article explores the connection between this common antihistamine and gastrointestinal side effects.

Quick Summary

While not one of its most common side effects in adults, levocetirizine can cause diarrhea, particularly in children [1.2.4]. This effect is generally mild, but it is important to understand its context and how to manage it.

Key Points

Direct Answer: Yes, levocetirizine can cause diarrhea, but it is an uncommon side effect in adults and more common in children and infants [1.3.2, 1.2.4].
Incidence Rate: In clinical trials, diarrhea was reported in 13% of infants (6-11 months) and 4% of young children (1-5 years) taking the medication [1.2.1].
Other GI Effects: Besides diarrhea, levocetirizine may also cause vomiting, constipation, and nausea, though these are also not among the most frequent side effects [1.3.2].
Primary Side Effects: The most commonly reported side effects for levocetirizine are sleepiness (somnolence), fatigue, and dry mouth [1.9.2].
Management: If diarrhea occurs, it's crucial to stay hydrated. If the symptom is severe, persistent, or bloody, consult a healthcare provider [1.2.4, 1.10.2].

Understanding Levocetirizine and Its Role

Levocetirizine, sold under brand names like Xyzal, is a second-generation antihistamine used to relieve symptoms of allergic rhinitis (hay fever) and hives [1.4.1, 1.4.2]. As an antihistamine, its primary function is to block the effects of histamine, a substance produced by the body during an allergic reaction [1.4.1]. Histamine is responsible for common allergy symptoms like sneezing, itching, runny nose, and watery eyes [1.4.1]. Unlike first-generation antihistamines, levocetirizine does not readily cross the blood-brain barrier, making it significantly less likely to cause drowsiness [1.2.4].

The Link: Does Levocetirizine Cause Diarrhea?

Yes, diarrhea is a recognized side effect of levocetirizine, although its incidence varies significantly by age [1.3.2]. According to prescribing information, diarrhea is more commonly reported in pediatric populations [1.2.4, 1.11.2].

Infants (6 to 11 months): Clinical trials showed that 13% of infants taking levocetirizine experienced diarrhea, compared to 4% in the placebo group [1.2.1, 1.2.2].
Children (1 to 5 years): In this age group, 4% of children treated with levocetirizine reported diarrhea [1.2.1, 1.2.2].
Adults and Adolescents (12+ years): For adults, diarrhea is listed as a 'common' side effect, defined as occurring in 1% to 10% of users, but it is not among the most frequently reported issues like somnolence (sleepiness) and dry mouth [1.3.2, 1.9.2].

The exact mechanism by which levocetirizine causes diarrhea isn't fully understood. While it primarily targets H1 histamine receptors to control allergies, histamine receptors also exist in the gastrointestinal tract. It's theorized that the drug's interaction with these receptors could alter gut motility or fluid secretion, leading to side effects like diarrhea or constipation [1.3.2].

Other Gastrointestinal and Common Side Effects

Beyond diarrhea, levocetirizine can cause other gastrointestinal issues, though they are also generally uncommon. These include vomiting, constipation, and nausea [1.3.2, 1.11.4].

The most common side effects across all age groups include [1.9.2, 1.11.2]:

Somnolence (sleepiness or drowsiness)
Fatigue or weakness
Dry mouth
Nasopharyngitis (sore throat and runny nose)
Fever (more common in children)
Cough (more common in children)

Comparing Antihistamines: A Look at GI Side Effects

When choosing an allergy medication, comparing side effect profiles is crucial. Levocetirizine is the active R-enantiomer of cetirizine (Zyrtec), meaning they are very similar chemically [1.12.1].


Medication	Generic Name	Generation	Common GI Side Effects	Notes
Xyzal	Levocetirizine	Second/Third	Diarrhea (esp. in children), constipation, vomiting, dry mouth [1.3.2].	Gastrointestinal issues are considered rare in adults [1.5.1].
Zyrtec	Cetirizine	Second	Diarrhea (esp. in children), stomach upset [1.5.2, 1.7.1].	Chemically very similar to levocetirizine, similar side effect profile [1.12.3].
Allegra	Fexofenadine	Second	Nausea, stomach pain [1.6.1, 1.6.3].	Generally considered one of the least sedating options [1.12.4].
Claritin	Loratadine	Second	Nausea, stomach pain [1.6.1, 1.6.3].	Also has a low risk of drowsiness [1.6.4].

Managing Diarrhea and Other Side Effects

If you experience diarrhea while taking levocetirizine, the symptoms are often mild and may resolve as your body adjusts to the medication [1.7.1].

Stay Hydrated: The most important step is to drink plenty of fluids to prevent dehydration [1.2.4, 1.7.1]. Water, broth, or electrolyte solutions are good choices.
Monitor Symptoms: Keep track of the frequency and severity. Most mild, medication-related diarrhea is short-lived.
Consider Timing: Taking the medication with food might help some individuals, though it can be taken with or without food [1.4.3].
Avoid Irritants: While experiencing diarrhea, it's wise to avoid other foods and substances that can irritate the GI tract, such as very spicy foods, high-fat meals, and alcohol.
Talk to a Pharmacist: For mild cases, an over-the-counter anti-diarrheal medication might be an option, but it's best to consult a pharmacist or doctor first [1.7.1].

When to Contact a Doctor

A healthcare provider should be consulted if you experience any of the following [1.10.2, 1.10.4]:

Diarrhea that is severe, bloody, or lasts for more than a few days.
Signs of dehydration, such as dizziness, decreased urination, and extreme thirst.
Any other serious side effects, such as difficulty urinating, hallucinations, or signs of a severe allergic reaction (hives, swelling, trouble breathing) [1.11.4].

Conclusion

While levocetirizine can cause diarrhea, it is not a frequent side effect for adults, occurring more commonly in infants and young children [1.2.1, 1.11.2]. The effect is typically mild and transient. Understanding this potential side effect allows for better management, which primarily involves staying hydrated and monitoring symptoms [1.2.4]. If the diarrhea is persistent or severe, or accompanied by other concerning symptoms, it is essential to seek medical advice [1.10.2]. As with any medication, balancing the therapeutic benefits against potential side effects is a key conversation to have with a healthcare provider.

For more detailed prescribing information, you can review the official FDA label for Levocetirizine: https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/022064s038,022157s020lbl.pdf [1.8.1].

Frequently Asked Questions

Diarrhea is more common in children than adults. Clinical studies showed it occurred in up to 13% of infants (6-11 months) and 4% of children (1-5 years) [1.2.1]. For adults, it's listed as a side effect that can occur in 1-10% of users but is less frequent than sleepiness or dry mouth [1.3.2].

The exact reason isn't fully established, but it is believed to be related to the drug's effect on histamine receptors in the gastrointestinal tract, which can influence gut motility and secretions [1.4.1].

The most common side effects for adults are somnolence (drowsiness), fatigue, and dry mouth [1.9.2]. In children, fever and cough are also common side effects in addition to drowsiness [1.11.2].

You should focus on drinking plenty of fluids to prevent dehydration [1.2.4]. The diarrhea is often mild and may go away as your body adjusts. If it is severe, lasts more than a few days, or contains blood, you should contact your doctor [1.10.2].

Levocetirizine and its parent drug cetirizine (Zyrtec) are both noted to cause diarrhea, especially in children [1.5.2, 1.11.2]. Other second-generation antihistamines like fexofenadine (Allegra) and loratadine (Claritin) are more commonly associated with nausea or general stomach pain [1.6.3].

Yes, levocetirizine is approved for use in children, with specific dosages available for infants as young as 6 months [1.4.3]. However, you should always consult a pediatrician for the correct dose and to discuss potential side effects like diarrhea, fever, and cough [1.11.2].

You should see a doctor if side effects are severe, persistent, or significantly interfere with daily life [1.10.1]. Seek immediate medical help for signs of a severe allergic reaction, like swelling and difficulty breathing, or other serious effects like trouble urinating [1.10.2, 1.11.4].