ModerateCaution
Melatonin
Melatonin can add to levocetirizine-related somnolence and next-day impairment.
Recommendation: Use cautiously, especially when driving, working at heights, or caring for dependents overnight.
Levocetirizine
Prescription ·Strong evidence ·Reviewed May 2026
Levocetirizine is the active R-enantiomer of cetirizine and is used for allergic rhinitis and chronic idiopathic urticaria. It is generally less sedating than first-generation antihistamines but can still cause somnolence and requires renal dose adjustment because it is substantially excreted by the kidneys.
What it's good for
The bottom line
Evidence rating strong. Most-documented uses: relief of seasonal allergic rhinitis symptoms, relief of perennial allergic rhinitis symptoms, reduction of itching and hives in chronic idiopathic urticaria. 3 sources indexed (2006–2026), with 3 interaction records on file.
The science
How it works, mechanistically.
Core mechanism
Levocetirizine selectively antagonizes peripheral histamine H1 receptors, reducing histamine-mediated itching, sneezing, rhinorrhea, and wheal-and-flare reactions. It has limited central penetration compared with older antihistamines but still can impair alertness in some patients. Renal elimination makes exposure higher in kidney impairment.1,3
Class
Second-generation H1 antihistamine
Dosing
Dosing & protocol.
Common range
Adults and adolescents: 5 mg orally once daily in the evening; some patients may respond to 2.5 mg once daily. Dose reduction is required in renal impairment.
Recommended form
Oral tablet or oral solution, often taken in the evening
May be taken with or without food. Avoid alcohol and other sedating products if drowsiness occurs.
Safety
Full safety detail.
Side effects
- Somnolence
- Fatigue
- Dry mouth
- Nasopharyngitis
- Headache
- Dizziness
- Urinary retention in susceptible patients
- Hypersensitivity reactions rarely
Interactions
Interaction records.
ModerateCaution
L-Theanine
L-theanine may compound fatigue or reduced alertness from levocetirizine.
Recommendation: Monitor alertness and avoid combining with other sedatives if drowsiness develops.
ModerateCaution
Ashwagandha
Ashwagandha can be sedating in some users and may add to antihistamine-related drowsiness.
Recommendation: Avoid starting high doses when assessing levocetirizine tolerability; stop if excessive sedation occurs.
Sources
Sources, by evidence tier.
Numbered references. Citations throughout the page link here.
Randomized controlled trials
1- 1Levocetirizine for the treatment of chronic idiopathic urticariaNeeds reviewNo linkKapp A et al. · Allergy · 2006
Controlled data support reduction of pruritus and wheal symptoms with levocetirizine.
Reviews & position papers
1- 2Allergic Rhinitis and its Impact on Asthma guidelinesNeeds reviewNo linkBousquet J et al. · Journal of Allergy and Clinical Immunology · 2020
Guidelines support modern H1 antihistamines for rhinitis symptom control with attention to sedation.
Reference material
1- 3Levocetirizine Dihydrochloride Tablets US Prescribing InformationNeeds reviewURLU.S. National Library of Medicine · DailyMed · 2026
Labeling describes 5 mg evening dosing, renal impairment adjustments, somnolence, fatigue, and avoidance of alcohol or CNS depressants.
Keep exploring
Deep dives & adjacent profiles.
This page is educational. Do not start, stop, or change a supplement or medication based on it without checking with a qualified healthcare professional.
Use this with your stack
Levocetirizine in NutriStack.
Add it to your stack, see how it interacts with everything else you take, and get a Stack Score that updates the moment it does.