Levocetirizine

What it is

Levocetirizine is a second-generation H1-antihistamine and is the active mirror-image half (the R-enantiomer) of cetirizine. The label describes it as the active enantiomer of cetirizine whose principal effects are mediated by selective inhibition of H1 receptors, with roughly twice cetirizine's affinity for the human H1 receptor in laboratory binding studies, though it adds that the clinical relevance of that is unknown. It is sold as tablets and oral solution, by prescription and over the counter, under names including Xyzal.

What the research says

Randomised placebo-controlled trials show levocetirizine reduces nasal and eye symptoms in allergic rhinitis and reduces itch in chronic idiopathic urticaria, with differences from placebo that are statistically clear but modest in size on the scales used. A Cochrane review of antihistamines for chronic hives rated the evidence low quality and found levocetirizine's results inconsistent across doses. Drowsiness is the common harm, dose-related and roughly three times the placebo rate at 5 mg, but on-road driving and psychometric testing at that dose found no measurable impairment. The distinctive harm is on the way out: after months or years of use, stopping can trigger new, sometimes severe, generalised itching.

Evidence grade: Well established.

How it works

Drug class: Second-generation (peripherally selective) H1-receptor antihistamine; piperazine derivative, the R-enantiomer of cetirizine

When an allergic reaction starts, mast cells dump histamine, and histamine docking onto H1 receptors is what produces the sneezing, streaming nose, itchy eyes and hives. Levocetirizine sits on those H1 receptors and blocks histamine from docking. Because it crosses into the brain far less than older antihistamines, it blocks the peripheral reaction with much less sedation. In volunteers it suppressed the weal and flare raised by injecting histamine into the skin, with the effect lasting at least 24 hours. (Source 1)

What it is used for

• Four randomised placebo-controlled trials in 1,729 adults and adolescents showed all tested doses beat placebo on total symptom score (difference 1.10 to 1.22 points, all p<0.001), with onset within one hour of a 5 mg dose. A separate 551-patient six-month trial showed sustained symptom and quality-of-life benefit. One warning about the label itself: section 1.1 of this prescription tablet label writes the perennial allergic rhinitis indication only for "children 6 months to 2 years of age", while the label's own summary of section 1 gives perennial allergic rhinitis with no age limit, the dosing section covers only ages 6 and over, and the one strength made is a 5 mg scored tablet. A 6-month age floor cannot be taken at face value for a tablet, and section 1.1 should not be read as the adult indication; adult hay fever use of levocetirizine sits on over-the-counter labelling. Evidence: established. (Source 2)
• Two four-week randomised placebo-controlled trials in 423 adults showed levocetirizine reduced itch severity more than placebo at 2.5, 5 and 10 mg, with wheal number and size also improving. A Cochrane review of 73 antihistamine studies rated the overall evidence low quality, found levocetirizine 5 mg effective in the intermediate but not short term, and concluded no single antihistamine stands out as most effective. Evidence: limited. (Source 3)
• Raising the dose above the licensed 5 mg is common practice in refractory hives. The Cochrane review found levocetirizine 20 mg a day did achieve complete suppression of urticaria compared with placebo in the short term (RR 20.87, 95% CI 1.37 to 317.60), but 10 mg did not, and the confidence interval shows this rests on a single very small study. The label's dose-ranging trial also showed 10 mg gave a larger itch reduction than 5 mg. Safety data at these doses are thin. Evidence: limited. (Source 4)
• Approval in children under 12 rests on extrapolation from adult trials matched on blood levels, not on efficacy trials in children. The label states plainly that there are no clinical efficacy trials at 2.5 mg under 12 years and none at 1.25 mg in children 6 months to 5 years, and no efficacy trials at all in children with chronic idiopathic urticaria. Safety was studied, in trials of 2 to 6 weeks plus one 18-month trial in 255 children aged 12 to 24 months. Evidence: unknown. (Source 5)

Interactions

• Alcohol (label): The label says concurrent use of levocetirizine with alcohol or other central nervous system depressants should be avoided, because alertness can fall further and central nervous system performance be further impaired than with either alone. This is a labelled warning rather than a measured interaction study in the sections we read. (Source 6)
• Other central nervous system depressants (sedatives, opioids, sleep aids) (label): Same mechanism as alcohol: additive reduction in alertness. The label groups them together and advises against concurrent use, and separately warns against hazardous occupations needing full alertness. (Source 6)
• Ritonavir (pharmacokinetic study): Studied with racemic cetirizine rather than levocetirizine itself: ritonavir raised cetirizine exposure by about 42%, lengthened its half-life by 53% and cut clearance by 29%. Cetirizine did not affect ritonavir. (Source 7)
• Theophylline (pharmacokinetic study): A 400 mg dose of theophylline produced a small (about 16%) fall in cetirizine clearance in a study of racemic cetirizine, and the label warns higher theophylline doses could have a greater effect. (Source 8)
• Erythromycin, azithromycin, ketoconazole, cimetidine, pseudoephedrine, antipyrine (pharmacokinetic study): These were tested with racemic cetirizine and no interaction was found, which is reassuring for drugs that commonly interact through liver enzymes. (Source 8)
• Grapefruit juice, St John's wort and other supplements acting on liver drug-metabolising enzymes (theoretical): No study of these with levocetirizine exists. The reason to expect little effect is that levocetirizine is barely metabolised: the label states in vitro data indicate it is unlikely to produce pharmacokinetic interactions through inhibition or induction of liver drug-metabolising enzymes, and that no in vivo drug interaction studies have been done with levocetirizine at all. Treat the absence of a signal as untested rather than proven safe. (Source 9)
• A high-fat meal (pharmacokinetic study): Food changes the shape but not the size of the exposure: a high-fat meal delayed the peak by about 1.25 hours and cut peak concentration by about 36%, with no change in total exposure, so the label allows dosing with or without food. (Source 10)

Stopping it

• Stopping levocetirizine after long-term use can cause new, sometimes severe, widespread itching within a few days, in people who had no itch before starting. This warning was added to the US label in April 2025. (Source 11)
• The label's own suggestion for managing it is pharmacological rather than reassurance: symptoms may improve by restarting the drug or tapering it rather than stopping outright. (Source 11)
• The FDA case series behind this warning is the strongest evidence that the effect is real rather than coincidental: of 55 patients who stopped cetirizine again after restarting it, 54 had the itch come back. Median use before stopping was 24 months and median time to onset was 2 days. (Source 12)
• The FDA authors concluded there is an association between stopping cetirizine and developing itching, that the mechanism is unknown, and that patients and prescribers should know about it given how widely the drug is used. (Source 13)
• A single case report suggests bridging with a different antihistamine for a few days may allow stopping without rebound, but this is one patient and the authors say larger studies are needed to confirm it. (Source 14)
• There is no evidence of physical dependence, tolerance or a classical withdrawal syndrome with levocetirizine. The discontinuation problem recorded in the label and the FDA series is new-onset pruritus, listed among skin reactions in postmarketing experience, not a dependence syndrome. (Source 15)

What goes wrong

Drowsiness is the commonest harm and it is dose-related: somnolence in 6% on 5 mg versus 2% on placebo, and it was the most frequent reason for stopping. (Source 16)

• Randomized trial, Certainty not rated.
• Size: 1,070 on 5 mg, 421 on 2.5 mg and 912 on placebo in eight pooled placebo-controlled trials; 2,708 patients in 14 controlled trials overall.
• Who: patients aged 12 and over with allergic rhinitis or chronic idiopathic urticaria.
• How long: 1 to 6 weeks for the pooled short-term safety analysis.
• Result: somnolence 61/1070 (6%) on 5 mg and 22/421 (5%) on 2.5 mg versus 16/912 (2%) on placebo (an absolute excess of about 4 percentage points at 5 mg, arithmetic from the reported figures); fatigue 4% vs 2%; dry mouth 2% vs 1%; somnolence was the most common reaction leading to discontinuation at 0.5%. Overall, 42% on 5 mg had at least one adverse event versus 43% on placebo.
• Funding: manufacturer trials reported in the FDA-approved label.

Limit of this finding: Table 1's own caption says it lists only reactions reported in at least 2% of people taking levocetirizine and more often than on placebo, but two of its cells break that rule: fatigue on the 2.5 mg dose is 5 cases (1%) against 20 (2%) on placebo, and pharyngitis on 5 mg is 12 (1%) against 9 (1%) on placebo. The caption describes the table as a whole, not every cell in it, so a single cell should not be read as meaning that reaction was commoner than placebo at that dose. The somnolence figures - 6% on 5 mg against 2% on placebo - do meet the caption, and nasopharyngitis at 6% on 2.5 mg does too.

Somnolence with levocetirizine dihydrochloride showed dose ordering between tested doses of 2.5, 5 and 10 mg and was the most common adverse reaction leading to discontinuation (0.5%). Table 1 lists adverse reactions that were reported in greater than or equal to 2% of subjects aged 12 years and older exposed to levocetirizine dihydrochloride 2.5 mg or 5 mg in eight placebo-controlled clinical trials and that were more common with levocetirizine dihydrochloride than placebo. Table 1: Adverse Reactions Reported in ≥ 2%* of Subjects Aged 12 Years and Older Exposed to Levocetirizine Dihydrochloride 2.5 mg or 5 mg Once Daily in Placebo-Controlled Clinical Trials 1 to 6 Weeks in Duration Adverse Reactions Levocetirizine Dihydrochloride 2.5 mg (n= 421) Levocetirizine Dihydrochloride 5 mg (n = 1070) Placebo (n = 912) Somnolence 22 (5%) 61 (6%) 16 (2%) Nasopharyngitis 25 (6%) 40 (4%) 28 (3%) Fatigue 5 (1%) 46 (4%) 20 (2%) Dry Mouth 12 (3%) 26 (2%) 11 (1%) Pharyngitis 10 (2%) 12 (1%) 9 (1%) * Rounded to the closest unit percentage

Stopping levocetirizine after long-term use can cause new, sometimes severe, generalised itching within days, a harm added to the US label in April 2025. (Source 11)

• Case series, Certainty not rated.
• Size: not quantified in the label; reported cases described as infrequent.
• Who: people who had taken levocetirizine long-term (months to years) and who did not have itching before starting it.
• How long: itching begins within a few days of stopping.
• Result: no rate given; the label states some cases were serious, with widespread severe pruritus, and that symptoms may improve on restarting or tapering.
• Funding: not applicable (FDA-approved labelling based on postmarketing reports)

Pruritus occurred within a few days of discontinuing levocetirizine dihydrochloride tablets among patients who used levocetirizine dihydrochloride tablets long-term (e.g., few months to years). Reported cases of pruritus were infrequent, but some were serious with patients experiencing widespread severe pruritus

An FDA analysis of adverse event reports and the literature for cetirizine, of which levocetirizine is the active half, identified 146 cases of itching after stopping, and in 54 of 55 rechallenged patients the itching came back. (Source 12)

• Case series, Very low certainty.
• Size: 146 cases identified in the FAERS database and medical literature up to 24 April 2017.
• Who: cetirizine users reported to the FDA or described in the literature; median age 38 years (range 6 to 71), predominantly female.
• How long: median duration of cetirizine use before stopping 24 months (range 0.3 to 172.2 months); median time to itch onset 2 days (range 0.5 to 5 days)
• Result: 54 of 55 cases that stopped cetirizine again after restarting reported the itching recurred; the mechanism is unknown.
• Funding: FDA authors analysing the agency's own adverse event reporting system; no external funding stated.

Of the 55 cases that reported discontinuation of cetirizine again after restarting, 54 reported pruritus recurrence.

Rarer but serious harms reported after marketing include seizures in people with and without epilepsy, hepatitis, anaphylaxis, movement disorders, urinary retention and suicidal ideation; rates cannot be estimated from these reports. (Source 17)

• Case series, Very low certainty.
• Size: not quantifiable; spontaneous postmarketing reports from a population of uncertain size.
• Who: people taking levocetirizine after approval, plus events reported with racemic cetirizine that the label says could also occur.
• How long: not applicable.
• Result: no rates can be derived; the label states it is not always possible to estimate frequency or establish causality from such reports.
• Funding: not applicable (FDA-approved labelling)

Nervous system disorders: dizziness, dysgeusia, febrile seizure, movement disorders (including dystonia and oculogyric crisis), paraesthesia, seizure (reported in subjects with and without a known seizure disorder), tremor • Psychiatric disorders: aggression and agitation, depression, hallucinations, insomnia, nightmare, suicidal ideation • Renal and urinary disorders: dysuria, urinary retention • Respiratory, thoracic, and mediastinal disorders: dyspnea

Urinary retention has been reported, and the label tells prescribers to use caution in people predisposed to it and to stop the drug if it happens. (Source 18)

• Case series, Very low certainty.
• Size: not quantified (postmarketing reports)
• Who: people taking levocetirizine, particularly those with spinal cord lesions or an enlarged prostate.
• How long: not specified.
• Result: no rate given.
• Funding: not applicable (FDA-approved labelling)

Levocetirizine dihydrochloride should be used with caution in patients with predisposing factors of urinary retention (e.g. spinal cord lesion, prostatic hyperplasia) as levocetirizine dihydrochloride may increase the risk of urinary retention.

A published case report describes levocetirizine, a drug normally used to treat skin reactions, itself causing a fixed drug eruption. (Source 19)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: a patient reported to a pharmacovigilance centre; causality assessed as probable and preventable.
• How long: not stated.
• Result: a single case; no rate can be inferred from one report.
• Funding: reported through an adverse drug reaction monitoring centre; funding not stated.

FDE due to levocetirizine, as well as with cetirizine, is less common in the literature. This case was reported to our ADR Monitoring Center and causality was assessed as probable and preventable. This case shows that antihistamines such as levocetirizine can trigger FDE in susceptible individuals. Improving clinical awareness through robust Pharmacovigilance activities, educating patients about triggers, and discouraging self-medication are crucial for preventing recurrence.

A case report of rebound itching and hives after stopping long-term over-the-counter cetirizine found a short bridge with a different antihistamine allowed the drug to be stopped, though the authors stress larger studies are needed. (Source 14)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: a Chinese man in his 50s with chronic urticaria who had taken over-the-counter cetirizine regularly for two years.
• How long: symptoms emerged two to three days after each attempt to stop.
• Result: a single case; switching to loratadine and chlorpheniramine for three days before an as-needed regimen avoided recurrence.
• Funding: not stated.

There have been increasing reports showing increased risk of rebound pruritus following discontinuation of long-term antihistamine use in the United States and the Netherlands. However, evidence on this condition and its management among Asian populations remains limited. We report the case of a Chinese male in his 50s with a background of hypertension, hyperlipidaemia, and chronic urticaria who had been regularly taking over-the-counter cetirizine for the past two years. He presented with recurrent urticaria, characterized by wheals and severe pruritus over his forearms, emerging two to three days after each cetirizine discontinuation attempt. A diagnosis of rebound pruritus and urticaria post-discontinuation of cetirizine was made. Through shared decision-making, he was switched to loratadine and chlorpheniramine for three days before transitioning to an "as-needed" regimen without recurrence of pruritus or urticaria. While the pathophysiology of rebound pruritus and urticaria post-discontinuation of chronic cetirizine use remains poorly understood, this case report suggests that the phenomenon may be drug-specific rather than a class-specific adverse effect. Larger studies are necessary to confirm if a temporary switch and short-term bridging with alternative antihistamines offer a safer discontinuation strategy for patients on chronic cetirizine.

What the evidence supports

In placebo-controlled dose-ranging trials in perennial allergic rhinitis, all three levocetirizine doses beat placebo on total symptom score, and 2.5 mg did as well as 10 mg. (Source 2)

• Randomized trial, Certainty not rated.
• Size: 517 patients in the trial reported in the label's Table 4 (133 on 2.5 mg, 127 on 5 mg, 129 on 10 mg, 128 on placebo); 1,729 patients across the four rhinitis trials.
• Who: adults and adolescents aged 12 and over with symptoms of perennial allergic rhinitis.
• How long: 4 weeks in the dose-ranging trials; a separate 6-week and a 6-month trial also ran.
• Result: difference from placebo in reflective total symptom score (0-12 scale): 2.5 mg 1.17 (95% CI 0.71-1.63), 5 mg 1.22 (0.76-1.69), 10 mg 1.10 (0.64-1.57), all p<0.001; on-treatment adjusted means 4.12, 4.07 and 4.19 versus 5.29 on placebo.
• Funding: manufacturer trials reported in the FDA-approved label; funding not separately stated.

In these trials, each of the three doses of levocetirizine dihydrochloride demonstrated greater decrease in the reflective total symptom score than placebo and the difference was statistically significant for all three doses in the two studies.

A six-month double-blind placebo-controlled trial in 551 patients with persistent allergic rhinitis found levocetirizine 5 mg improved quality of life and symptom scores throughout. (Source 20)

• Randomized trial, Certainty not rated.
• Size: 551 patients randomised; 421 completed the full study.
• Who: adults with persistent rhinitis sensitised to both grass pollen and house dust mite, multicentre and multinational.
• How long: 6 months, with co-primary endpoints over the first 4 weeks.
• Result: Rhinoconjunctivitis Quality of Life Questionnaire overall score and Total 5 Symptoms Score both improved from week 1 to 6 months, all p values <.001; Short Form 36 summary scores were also improved versus placebo. The trial also reports lower overall costs of disease on levocetirizine, but the abstract gives its two cost figures without labels or a currency, so no per-group cost number is cited here.
• Funding: not stated in the abstract; the trial is named after the manufacturer's brand (the Xyzal in Persistent Rhinitis Trial), so an industry-sponsored trial should be assumed unless the full paper says otherwise.

Limit of this finding: The trial's cost sentence cannot be read off the abstract. It runs 'Treatment cessation because of lack of effect, comorbidities, and overall costs of disease, and comorbidities per working patient per month (160.27 vs 108.18) were lower in the levocetirizine group' - it lists comorbidities twice, gives the two figures with no currency and no group labels, and then says the levocetirizine group was lower. If the first number were levocetirizine's the sentence would contradict itself. In the full paper the placebo figure is given first. Read this as the authors reporting lower disease costs on levocetirizine, and do not read the bare pair of numbers as a per-group cost comparison.

Levocetirizine significantly improved both the Rhinoconjunctivitis Quality of Life Questionnaire overall score and the Total 5 Symptoms Score from week 1 to 6 months (all P values <.001).

In two placebo-controlled trials in chronic idiopathic urticaria, levocetirizine reduced itch severity more than placebo at every dose tested, with the largest effect at 10 mg. (Source 3)

• Randomized trial, Certainty not rated.
• Size: 423 patients across the two trials, of whom 146 received 5 mg once daily; dose-ranging arms 69, 62, 55 and 60.
• Who: adults aged 18 to 85 with chronic idiopathic urticaria; more than 90% white, mean age 41.
• How long: 4 weeks each.
• Result: difference from placebo in reflective pruritus severity score (0-3 scale): 2.5 mg 0.82 (95% CI 0.58-1.06), 5 mg 0.91 (0.66-1.16), 10 mg 1.11 (0.85-1.37), all p<0.001; in the second trial 5 mg gave 0.62 (0.38-0.86)
• Funding: manufacturer trials reported in the FDA-approved label; funding not separately stated.

In this trial, each of the three doses of levocetirizine dihydrochloride demonstrated greater decrease in the reflective pruritus severity score than placebo and the difference was statistically significant for all three doses (see Table 6).

What the evidence does not support

A Cochrane review of H1-antihistamines for chronic spontaneous urticaria found levocetirizine's results inconsistent across doses and time frames, with low-quality evidence overall and no antihistamine standing out as best. (Source 4)

• Systematic review, Low certainty.
• Size: 73 studies with 9,759 participants identified; 34 studies provided data for 23 comparisons.
• Who: people with chronic spontaneous urticaria.
• How long: short-term (up to two weeks) and intermediate-term (over two weeks up to three months)
• Result: levocetirizine 20 mg short-term beat placebo for complete suppression (RR 20.87, 95% CI 1.37 to 317.60); 5 mg worked in the intermediate term (RR 52.88, 3.31 to 843.81) but not short-term; 10 mg did not work short-term. The very wide confidence intervals reflect single small studies.
• Funding: not stated in the abstract (Cochrane review)

Levocetirizine 20 mg per day (short-term) was more effective for complete suppression of urticaria compared with placebo (RR 20.87,95% CI 1.37 to 317.60), and at 5 mg was effective in the intermediate term (RR 52.88, 95% CI 3.31 to 843.81) but not in the shortterm, nor was 10 mg effective in the short term.

The same Cochrane review says the evidence base behind all these antihistamines, including levocetirizine, is small, imprecise and low quality, and that evidence of improved quality of life was insufficient. (Source 21)

• Systematic review, Low certainty.
• Size: 73 studies, 9,759 participants; most comparisons rest on one or two small studies.
• Who: people with chronic spontaneous urticaria.
• How long: up to three months.
• Result: the review downgraded certainty for imprecision; unless otherwise stated the quality of evidence was low.
• Funding: not stated in the abstract (Cochrane review)

The quality of the evidence was affected by the small number of studies in each comparison and the small sample size for many of the outcomes, prompting us to downgrade the quality of evidence for imprecision (unless stated for each comparison, the quality of the evidence was low).

There are no efficacy trials of levocetirizine in children under 12; the approved paediatric doses rest on matching blood levels to adults, not on measured symptom benefit in children. (Source 5)

• Official position, Certainty not rated.
• Size: not applicable (absence of trials stated in the label; safety was studied in 243 children aged 6-12, 114 aged 1-5 and 45 aged 6-11 months)
• Who: children under 12 years of age.
• How long: safety trials ran 2 to 6 weeks; an 18-month safety trial ran in 255 children aged 12 to 24 months.
• Result: no efficacy trials at 2.5 mg under 12 years and none at 1.25 mg in 6 months to 5 years; efficacy is extrapolated from adult trials on pharmacokinetic comparisons.
• Funding: manufacturer data reported in the FDA-approved label.

There are no clinical efficacy trials with levocetirizine dihydrochloride 2.5 mg once daily in pediatric patients under 12 years of age, and no clinical efficacy trials with levocetirizine dihydrochloride 1.25 mg once daily in pediatric patients 6 months to 5 years of age.

In an on-road driving test, levocetirizine 5 mg did not impair driving, while diphenhydramine did; this is evidence against the sedation that older antihistamines cause, not evidence of no sedation at all. (Source 22)

• Randomized trial, Certainty not rated.
• Size: 48 healthy volunteers.
• Who: healthy volunteers in a double-blind, placebo-controlled, randomised crossover trial driving in normal traffic.
• How long: dosing on days 1 to 4, with the standardised driving test on day 1 and day 4.
• Result: standard deviation of lateral position after levocetirizine was equivalent to placebo on day 1 (-0.66 cm; +1.12 cm) and day 4 (-0.37 cm; +1.28 cm), within the prespecified equivalence range of -2.6 to +2.6 cm; diphenhydramine differed significantly from placebo on both days.
• Funding: not stated in the abstract.

SDLP after levocetirizine was equivalent to placebo on both day 1 (-0.66 cm; +1.12 cm) and day 4 (-0.37 cm; +1.28 cm).

In a three-way crossover study in 19 healthy men, the authors report that levocetirizine 5 mg did not change the study's main measure of brain function, and that body sway, learning and memory and self-rated alertness were no different from placebo, while diphenhydramine increased body sway and reduced alertness. (Source 23)

• Randomized trial, Certainty not rated.
• Size: 19 healthy male volunteers.
• Who: healthy men in a three-way crossover trial of levocetirizine 5 mg, diphenhydramine 50 mg and placebo.
• How long: once daily for 5 consecutive days.
• Result: the abstract states that critical flicker fusion, the primary endpoint, was not modified regardless of the dosing scheme, and prints two unlabelled values three hours after dosing on day 1, -1.62 Hz (-2.61, -0.64) and -0.81 Hz (-1.80, 0.19); body sway and the learning memory test were similar to placebo, body sway increased with diphenhydramine, and alertness on a visual analogue scale fell with diphenhydramine 50 mg but not with levocetirizine.
• Funding: not stated in the abstract (study of the manufacturer's new drug)

Limit of this finding: The paper's own results sentence does not hold together. It says levocetirizine did not change the study's main measure of brain function (critical flicker fusion), but the two figures printed immediately after that statement carry no drug labels, and the first of them, -1.62 Hz (95% confidence interval -2.61 to -0.64), excludes zero, which is what a real change looks like. The sensible reading is that the first figure belongs to diphenhydramine, the older sedating antihistamine used as the comparison, and the second, -0.81 Hz (-1.80 to 0.19), to levocetirizine, but the abstract never says so and the full text could not be reached to settle it. So treat this as the authors reporting no sedation signal for levocetirizine on their main measure, and do not read the two numbers as showing which drug did what. The same sentence also records that choice reaction time fell on placebo as well as on levocetirizine, which is what getting better at a repeated test looks like rather than a drug effect.

levocetirizine did not modify the CFF (primary endpoint), regardless of the dosing scheme (-1.62 Hz [-2.61, -0.64] and -0.81 Hz [-1.80, 0.19], respectively, 3 h after dosing on day 1). CRT was decreased with both levocetirizine and placebo up to 5 h after dosing on day 1 and up to 3 h after dosing on day 5. Body sway data were similar with levocetirizine and placebo but increased with diphenhydramine. LMT was similar in all three groups. No relevant difference between placebo and levocetirizine was recorded by the subjects on their assessment of alertness using the VAS, whilst decreased alertness was reported following diphenhydramine 50 mg.

Where the research disagrees

How well levocetirizine works for chronic hives, and at what dose

• Manufacturer trials in the FDA-approved label, two four-week randomised placebo-controlled trials, 423 adults: "each of the three doses of levocetirizine dihydrochloride demonstrated greater decrease in the reflective pruritus severity score than placebo and the difference was statistically significant for all three doses" (Source 3)
• Cochrane review of H1-antihistamines for chronic spontaneous urticaria (2014), systematic review of 73 studies, 9,759 participants, with certainty downgraded to low for imprecision: "Levocetirizine at 5 mg in the intermediate but not short term was effective for complete suppression. Levocetirizine 20 mg was effective in the short term, but 10 mg was not." and "No single H1-antihistamine stands out as most effective." (Source 21)

Whether levocetirizine causes meaningful sedation

• Pooled manufacturer safety data in the FDA label, eight pooled placebo-controlled trials; somnolence 6% on 5 mg versus 2% on placebo: Somnolence was dose-ordered and was the commonest reason for stopping the drug: "Somnolence with levocetirizine dihydrochloride showed dose ordering between tested doses of 2.5, 5 and 10 mg and was the most common adverse reaction leading to discontinuation (0.5%)." (Source 16)
• On-road driving trial in normal traffic (2003), randomised, double-blind, placebo-controlled crossover trial in 48 healthy volunteers at 5 mg: "SDLP after levocetirizine was equivalent to placebo on both day 1 (-0.66 cm; +1.12 cm) and day 4 (-0.37 cm; +1.28 cm)." (Source 22)
• Psychometric crossover study in healthy men (2002), three-way crossover trial in 19 healthy male volunteers, 5 mg daily for 5 days, with diphenhydramine as positive control: levocetirizine "did not modify the CFF (primary endpoint), regardless of the dosing scheme" (Source 23)

How much

• Reference intake: There is no reference intake for an antihistamine; the dose is a prescriber's or label's instruction. As a position, the FDA prescription label (levocetirizine dihydrochloride tablets, label version published 2026) gives 5 mg once daily in the evening for chronic idiopathic urticaria in adults and children 12 and over, 2.5 mg for children 6 to 11, and staged reductions for kidney impairment. (Source 24)
• Upper limit: No upper limit in the nutritional sense exists. As a position, the label's maximum approved adult dose is 5 mg once daily, the 2.5 mg dose should not be exceeded in children 6 to 11 because their exposure is about twice adult levels, and the drug should not be given at all in end-stage renal disease or on haemodialysis. (Source 24)
• Studied: The label's rhinitis dose-ranging trials gave levocetirizine 2.5, 5 and 10 mg once daily in the evening for four weeks. (Source 2)
• Studied: The urticaria trials gave 2.5, 5 and 10 mg once daily in the evening for four weeks. (Source 3)
• Studied: The six-month XPERT trial gave levocetirizine 5 mg a day to adults with persistent rhinitis sensitised to grass pollen and house dust mite. (Source 25)
• Studied: The Cochrane urticaria review includes levocetirizine arms at 5, 10 and 20 mg a day, with 20 mg being well above the approved dose. (Source 4)
• Studied: The on-road driving study gave levocetirizine 5 mg against diphenhydramine 50 mg and placebo on four consecutive days. (Source 26)
• Studied: A QT study used a single 30 mg dose of levocetirizine; safety trials in children used 1.25 mg once or twice daily. (Source 27)

A common belief, and what the research shows

The belief: A non-sedating antihistamine like levocetirizine can be started and stopped freely, with nothing to come off.

What the research shows: Stopping is the one thing that needs care. The US label now carries a warning that "Cases of pruritus after discontinuation of levocetirizine dihydrochloride tablets have been reported in the postmarketing setting in patients where pruritus was not present before initiation of Levocetirizine dihydrochloride tablets." and that "Reported cases of pruritus were infrequent, but some were serious with patients experiencing widespread severe pruritus". The FDA case series found that "Of the 55 cases that reported discontinuation of cetirizine again after restarting, 54 reported pruritus recurrence." This is not physical dependence, but it does mean long-term users may not be able to simply stop.

Questions and answers

What is it?

Levocetirizine is a second-generation antihistamine. Chemically it is one half of cetirizine: cetirizine is a mixture of two mirror-image molecules, and levocetirizine is the one that does the work. The label calls it the active enantiomer of cetirizine, acting by selective inhibition of H1 receptors. It is sold as Xyzal and as generic levocetirizine dihydrochloride, in prescription and over-the-counter forms. (Source 1)

What does it do in the body?

It blocks the H1 histamine receptor, so the histamine released during an allergic reaction cannot trigger the sneezing, running nose, itching and hives it would otherwise cause. In healthy volunteers, 2.5 mg and 5 mg suppressed the weal and flare raised by injecting histamine into the skin, and the effect lasted at least 24 hours in children. It does not stop histamine being released; it stops the receptor responding. (Source 1)

Is it good or bad for you?

Mostly good and mild for the people it is prescribed to. It beat placebo on symptom scores in allergic rhinitis and on itch in chronic hives, and in on-road and psychometric testing at 5 mg it did not impair driving or cognition the way older antihistamines do. The main costs are drowsiness, which is dose-related (6% on 5 mg versus 2% on placebo), and a withdrawal problem: after months or years of use, stopping can bring on severe new itching. (Source 16)

How do you get more of it?

It is a medicine, not a nutrient, so there is nothing to top up. Where it is prescribed, the label's position for chronic hives in adults and children 12 and over is 5 mg once daily in the evening, with 2.5 mg enough for some, and reduced doses or avoidance in kidney impairment. It can be taken with or without food. Doses above 5 mg have been tested in trials but are not approved, and the dose is a prescriber's decision. (Source 24)

If it is harmful, what reduces it?

If levocetirizine is causing harm, it is stopped, but stopping has its own risk after long use. The label says if itching appears after stopping, symptoms may improve with restarting or tapering the drug. For urinary retention, the label's instruction is simply to discontinue. There is no antidote and the drug is cleared by the kidneys, so it leaves the body on its own once stopped. (Source 11)

Why might someone be low in it or missing it?

Nobody is naturally low in levocetirizine. Blood levels can be higher than intended in people with reduced kidney function, which is why the label stages the dose down from mild to severe impairment and rules the drug out entirely in end-stage kidney disease and dialysis; children aged 6 to 11 reach roughly double adult exposure on a 5 mg dose, which is why 2.5 mg is the ceiling for them. Levels can also rise about 42% with ritonavir. (Source 24)

Which whole foods contain it or feed it?

No whole food contains levocetirizine. Food matters only for timing: a high-fat meal delayed the peak by about 1.25 hours and lowered the peak concentration by about 36%, but did not change total exposure, so the label says it can be taken with or without food. There is no documented food that supplies or substitutes for the drug. (Source 10)

What happens if you do not have it?

Going without it means allergic symptoms run unopposed. In a six-month trial of 551 people with persistent allergic rhinitis, those on placebo had worse quality of life and symptom scores throughout and higher disease-related costs. In chronic hives, placebo groups still improved somewhat (itch score falling from 2.25 to 1.84 in one arm), so the drug adds to, rather than replaces, natural settling. Nothing dangerous happens from not taking it. (Source 28)

How can you test for it?

There is no clinical blood test for levocetirizine levels and none is needed. What gets measured is kidney function, because the dose depends on creatinine clearance and the drug is contraindicated below 10 mL/min. The pharmacological effect can be measured experimentally with a histamine skin weal-and-flare test, which levocetirizine suppresses, but the label states the clinical relevance of histamine weal skin testing is unknown. (Source 24)

References

1. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 12.1 Mechanism of Action. 2026. Read the source
2. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 14.1 Perennial Allergic Rhinitis (dose-ranging trials, Table 4). 2026. Read the source
3. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 14.2 Chronic Idiopathic Urticaria (trials and Table 6). 2026. Read the source
4. The Cochrane database of systematic reviews. H1-antihistamines for chronic spontaneous urticaria.. 2014. PMID 25397904, DOI 10.1002/14651858.cd006137.pub2. Read the source
5. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 14.1 Perennial Allergic Rhinitis (design and paediatric extrapolation). 2026. Read the source
6. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 5.1 Somnolence. 2026. Read the source
7. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 7.2 Ritonavir. 2026. Read the source
8. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 7.1 Antipyrine, Azithromycin, Cimetidine, Erythromycin, Ketoconazole, Theophylline, and Pseudoephedrine. 2026. Read the source
9. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 7 DRUG INTERACTIONS. 2026. Read the source
10. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 12.3 Pharmacokinetics (absorption, distribution and metabolism). 2026. Read the source
11. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 5.3 Risk of New Onset Pruritus After Discontinuation. 2026. Read the source
12. Therapeutic advances in drug safety. Pruritus after discontinuation of cetirizine.. 2019. PMID 31308927, DOI 10.1177/2042098619859996. Read the source
13. Therapeutic advances in drug safety. Pruritus after discontinuation of cetirizine.. 2019. PMID 31308927, DOI 10.1177/2042098619859996. Read the source
14. Cureus. Rebound Pruritus and Urticaria Post-discontinuation of Chronic Cetirizine Use: A Case Report.. 2025. PMID 41602253, DOI 10.7759/cureus.100214. Read the source
15. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 6.2 Postmarketing Experience (skin and cetirizine-class events). 2026. Read the source
16. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 6.1 Clinical Trials Experience (Table 1, adults and adolescents). 2026. Read the source
17. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 6.2 Postmarketing Experience. 2026. Read the source
18. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 5.2 Urinary Retention. 2026. Read the source
19. Indian journal of pharmacology. Levocetirizine-induced paradoxical fixed drug eruption: A case report with causality assessment.. 2026. PMID 42683994, DOI 10.4103/ijp.ijp_276_26. Read the source
20. The Journal of allergy and clinical immunology. Levocetirizine improves quality of life and reduces costs in long-term management of persistent allergic rhinitis.. 2004. PMID 15480324, DOI 10.1016/j.jaci.2004.05.070. Read the source
21. The Cochrane database of systematic reviews. H1-antihistamines for chronic spontaneous urticaria.. 2014. PMID 25397904, DOI 10.1002/14651858.cd006137.pub2. Read the source
22. Psychopharmacology. Driving ability after acute and sub-chronic administration of levocetirizine and diphenhydramine: a randomized, double-blind, placebo-controlled trial.. 2003. PMID 12721777, DOI 10.1007/s00213-003-1462-6. Read the source
23. British journal of clinical pharmacology. Lack of effect of single and repeated doses of levocetirizine, a new antihistamine drug, on cognitive and psychomotor functions in healthy volunteers.. 2002. PMID 12100225, DOI 10.1046/j.1365-2125.2002.01611.x. Read the source
24. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 2.2 Chronic Idiopathic Urticaria (dosage and renal adjustment). 2026. Read the source
25. The Journal of allergy and clinical immunology. Levocetirizine improves quality of life and reduces costs in long-term management of persistent allergic rhinitis.. 2004. PMID 15480324, DOI 10.1016/j.jaci.2004.05.070. Read the source
26. Psychopharmacology. Driving ability after acute and sub-chronic administration of levocetirizine and diphenhydramine: a randomized, double-blind, placebo-controlled trial.. 2003. PMID 12721777, DOI 10.1007/s00213-003-1462-6. Read the source
27. DailyMed / Glenmark Pharmaceuticals Inc., USA (FDA Structured Product Label). LEVOCETIRIZINE DIHYDROCHLORIDE tablet - 6.1 Clinical Trials Experience (exposure). 2026. Read the source
28. The Journal of allergy and clinical immunology. Levocetirizine improves quality of life and reduces costs in long-term management of persistent allergic rhinitis.. 2004. PMID 15480324, DOI 10.1016/j.jaci.2004.05.070. Read the source