Loratadine
Is It Right for You?
A complete guide to Loratadine — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Loratadine?
Loratadine is a second-generation, long-acting, non-sedating oral antihistamine available in tablets of 10 mg and as a syrup (5 mg/5 mL). It is one of the most widely used antihistamines globally for the management of allergic conditions and is available both over the counter and on prescription in the UK.
Unlike first-generation antihistamines (such as chlorphenamine), loratadine demonstrates high selectivity for peripheral histamine H1 receptors and has very poor penetration across the blood-brain barrier. This substantially reduces — though does not entirely eliminate — the sedation, anticholinergic effects, and cognitive impairment associated with older antihistamines, making loratadine suitable for use during the day and for people who cannot afford sedation.
Loratadine is rapidly converted in the body to its active metabolite desloratadine, which is responsible for the majority of its pharmacological activity and has a longer half-life — providing sustained 24-hour allergy control with once-daily dosing.
Loratadine is available both over the counter and on prescription in the UK. Prescription supply ensures clinical review of the diagnosis, assessment of appropriateness, and access for patients who require ongoing supply as part of their allergy management plan.
What Conditions Is Loratadine Used For?
Loratadine is indicated for:
relief of sneezing, nasal itch, rhinorrhoea, and itchy, watery eyes associated with seasonal allergen exposure (grass pollen, tree pollen, mould spores)
management of year-round nasal allergy symptoms triggered by persistent allergens such as house dust mite, animal dander, and mould
relief of itch and hives in acute and chronic urticaria (including chronic spontaneous urticaria, where once-daily loratadine is a first-line treatment)
relief of eye symptoms of allergic origin when topical treatment is not preferred or insufficient
Loratadine effectively blocks the effects of histamine at H1 receptors but does not modify the underlying allergic sensitisation or prevent mast cell degranulation. Allergen avoidance strategies and, for appropriate patients, allergen immunotherapy (desensitisation) address the root cause. For nasal symptoms, intranasal corticosteroids are more effective than antihistamines alone for the inflammatory component of allergic rhinitis and should be considered as first-line or add-on therapy.
How Does Loratadine Work?
Loratadine is a selective, long-acting antagonist at the histamine H1 receptor. Following oral absorption, it undergoes extensive first-pass metabolism to desloratadine — its active metabolite — which is the principal pharmacologically active compound:
H1 receptor competitive antagonism: Loratadine and desloratadine bind with high affinity and selectivity to peripheral H1 receptors on vascular smooth muscle, glandular epithelium, and sensory nerve endings. By occupying these receptors, they competitively prevent histamine — released from mast cells and basophils following allergen exposure — from exerting its effects: vasodilation, increased vascular permeability, glandular secretion, pruritus, and bronchoconstriction.
Peripheral selectivity and low CNS penetration: Loratadine and desloratadine are highly polar at physiological pH and are substrates for the efflux transporter P-glycoprotein at the blood-brain barrier, which actively limits their CNS penetration. This means H1 receptors in the central nervous system — which mediate arousal and wakefulness — are not significantly blocked at therapeutic doses, preserving wakefulness and minimising sedation.
Duration of action: Desloratadine has a half-life of approximately 27 hours, providing sustained histamine receptor blockade throughout the 24-hour period with once-daily dosing.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Can be taken with or without food. Food does not significantly affect the bioavailability of loratadine.
Take at the same time each day. Consistent once-daily dosing supports stable desloratadine plasma levels and all-day allergy control.
For seasonal allergic rhinitis, start before the pollen season begins. Beginning loratadine 1–2 weeks before the anticipated start of the pollen season provides better pre-emptive histamine receptor blockade than starting only after symptoms are established.
Combine with an intranasal corticosteroid for better rhinitis control. For moderate-to-severe allergic rhinitis, adding an intranasal steroid (e.g., fluticasone or mometasone) addresses the inflammatory component that antihistamines alone do not adequately treat — providing significantly better overall symptom control.
Loratadine is not appropriate for acute anaphylaxis. Antihistamines are adjunctive treatments in anaphylaxis but are not life-saving; intramuscular adrenaline (epinephrine) is the emergency treatment for anaphylaxis.
Side Effects of Loratadine
Most side effects are mild and resolve on their own. Serious side effects are rare but require immediate medical attention.
- Headache --- the most commonly reported side effect at therapeutic doses
- Somnolence --- less common than with first-generation antihistamines; reported by some patients, particularly at higher doses
- Dry mouth
- Fatigue
- Nausea
- Nervousness or excitability (particularly in children)
- Severe hypersensitivity reactions --- anaphylaxis, angioedema, and urticaria to the drug itself; rare but possible; seek immediate emergency care
- QT interval prolongation and arrhythmias --- loratadine at high doses or in the context of drug interactions (CYP3A4 inhibitors) may prolong the QT interval; clinically significant at supratherapeutic doses
- Hepatitis --- rare; jaundice, right upper quadrant pain, or elevated liver enzymes during loratadine therapy require clinical review
While loratadine is classified as a non-sedating antihistamine, a proportion of patients — particularly at the higher end of the dose range or in combination with other CNS-depressant medications — do experience meaningful drowsiness. Patients should assess their individual response before driving or operating machinery, particularly when first starting treatment.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting Loratadine
Increase plasma loratadine and desloratadine levels; the clinical significance at standard doses is limited due to loratadine's wide therapeutic margin, but QT prolongation risk may be modestly increased; monitor in patients at cardiac risk.
although loratadine itself has low sedative potential, combining with CNS depressants may produce additive effects in susceptible patients; advise caution with alcohol.
additive QT prolongation risk at supratherapeutic doses; routine clinical doses are not typically associated with clinically significant QT effects.
may modestly reduce the rate (but not extent) of loratadine absorption; no clinical significance.
Important Warnings
Loratadine is not appropriate as the primary or emergency treatment for anaphylaxis. Patients at risk of anaphylaxis must carry an adrenaline auto-injector (e.g., EpiPen). Antihistamines are adjunctive only in the management of anaphylaxis.
Loratadine is extensively metabolised by the liver. In patients with significant hepatic impairment, drug clearance is reduced and plasma levels increase; dosing should be reduced to 10 mg on alternate days and liver function monitored.
While loratadine is considered non-sedating, individual responses vary. Patients should assess their personal response before driving, particularly at the start of treatment. UK driving law requires that impaired driving due to any medication — including antihistamines — is not undertaken.
Animal data does not suggest teratogenicity. Loratadine is one of the antihistamines considered relatively acceptable for short-term use in pregnancy when an oral antihistamine is genuinely necessary, though specialist guidance should always be sought. Loratadine and desloratadine are excreted in breast milk; use with caution during breastfeeding and seek clinician guidance.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Loratadine FAQs
Loratadine is classified as a non-sedating antihistamine due to its very low CNS penetration compared to first-generation agents like chlorphenamine. In clinical trials, sedation rates are not significantly different from placebo at the 10 mg dose. However, a minority of patients — particularly those who are more sensitive to antihistamines or who combine loratadine with other medications — do report some drowsiness. Assess your own response before driving.
Both are second-generation antihistamines with similar efficacy for allergic rhinitis and urticaria. Cetirizine tends to have a slightly faster onset of action but is more likely to cause sedation in a proportion of patients. Loratadine is marginally less sedating on average but may be slightly slower in onset. The choice is often based on individual response — if one is not effective or causes drowsiness, the other may suit better.
Yes — loratadine is considered safe for continuous daily use throughout the allergy season or year-round for perennial allergy conditions. There is no evidence of meaningful tolerance developing with regular use. Clinical review should be undertaken periodically to reassess the ongoing need and to consider allergen immunotherapy for eligible patients.
Loratadine is one of the oral antihistamines regarded as relatively acceptable in pregnancy when treatment is genuinely needed, based on available safety data. However, the general principle is to use all medications in pregnancy only when clearly necessary and under clinician guidance. Intranasal corticosteroids for allergic rhinitis have very low systemic absorption and are generally preferred in pregnancy.
For moderate-to-severe allergic rhinitis, antihistamines alone frequently provide incomplete symptom control, particularly for nasal congestion (for which they are not effective). Combining loratadine with a daily intranasal corticosteroid (such as fluticasone or mometasone furoate) addresses the inflammatory component of allergic rhinitis far more effectively and is the recommended approach in current NICE and BSACI guidelines.