Loratadine causes drowsiness

LoratadineDrug groupsAntihistamines Loratadine is an active ingredient from the group of antihistamines of the 2nd generation, which is used to treat hay fever, allergic rhinitis, allergic conjunctivitis and nettle rash. In contrast to older antihistamines, loratadine causes less tiredness and its effects last for a long time, so it only has to be taken once a day. The most common possible adverse effects include indigestion, sore throat, cough, nosebleeds, rhinitis, upper respiratory tract infections, fatigue, dizziness, drowsiness, and nausea. Loratadine is a prodrug and is metabolized by CYP3A4 and CYP2D6.

synonymous: LoratadinumPhEur


Loratadine is commercially available in the form of tablets (Claritine®, Claritine® pollen, generics). It has been approved in Switzerland since 1991. The active metabolite desloratadine is also available (Aerius®, generics).

Structure and properties

Loratadine (C.22H23ClN2O2, Mr = 382.9 g / mol) is a white, crystalline powder that is practically insoluble in water. It is a prodrug and is biotransformed to desloratadine (descarboethoxyloratadine) and other metabolites, among other things. Loratadine is structurally related to other antihistamines such as cyproheptadine and to tricyclic antidepressants.


Loratadine (ATC R06AX13) has antihistamine and antiallergic properties and is less sedating than 1st generation antihistamines. It is not anticholinergic or cardiotoxic like astemizole or terfenadine. The effects are based on the selective antagonism of histamine H1 receptors.

Mechanism of action of antihistamines, click to enlarge. Illustration © PharmaWiki

Indications Dosage

According to the package insert. Since loratadine and its active metabolite have a long half-life, once-a-day administration is sufficient. The effect occurs faster if taken on an empty stomach.


The complete precautionary measures can be found in the medicinal product information sheet.


Loratadine is biotransformed by CYP3A4 and CYP2D6. Corresponding drug interactions are possible. According to the specialist information, the effects of alcohol are not increased.

unwanted effects

The most common possible adverse effects include:

  • Diarrhea, dry mouth, dyspepsia, increased appetite, sore throat
  • Cough, nosebleeds, rhinitis, upper respiratory infections
  • fatigue
  • Dizziness, drowsiness, nausea
see also

Antihistamines, hay fever, desloratadine

  • Pharmaceutical product information (CH, USA, D)
  • European Pharmacopoeia PhEur
  • Haria M., Fitton A., Peters D.H. Loratadine. A reappraisal of its pharmacological properties and therapeutic use in allergic disorders. Drugs, 1994, 48 (4), 617-37 Pubmed
  • Kaiser H.B., Gopalan G., Chung W. Loratadine provides early symptom control in seasonal allergic rhinitis. Allergy Asthma Proc, 2008, 29 (6), 654-8 Pubmed
  • Kay G.G., Harris A.G. Loratadine: a non-sedating antihistamine. Review of its effects on cognition, psychomotor performance, mood and sedation. Clin Exp Allergy, 1999, 29 Suppl 3, 147-50 Pubmed
  • Monroe E.W. Loratadine in the treatment of urticaria. Clin Ther, 1997, 19 (2), 232-42 Pubmed

Conflicts of Interest: None / Independent. The author has no relationships with the manufacturers and is not involved in the sale of the products mentioned.

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This article was last changed on April 23, 2020.
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