Cetirizine or Zyrtec is a non-sedating antihistamine. It is a metabolite of hydroxyzine, an sedating antihistamine.
Cetirizine or Zyrtec blocks histamine - specifically histamine 1 - sites. By blocking these sites histamine is not released and the effects of histamine on the body are not seen - runny nose, sneezing, watery eyes.
While Cetirizine or Zyrtec is classified as a non sedating antihistamine, it is able to cause some sedation, but much less than other antihistamines. As well, it can cause dry mouth.
Because Cetirizine or Zyrtec does have the potential to cause some sedation, it should be carefully used in situations where alertness is required - driving a car.
Cetirizine or Zyrtec has an additive effect with alcohol and thus should not be used with alcohol.
Cetirizine or Zyrtec does not interact with antibiotics such as erythromycin to cause heart beat irregularities.
Med Letter 1996;38(970):21
Allergy Clin Immunology 1996;97:617
J Allergy Clin Immunology 1995;96:174
J Allergy Clin Immunology 1995;95:923
The relevant product monographs must be regarded as the appropriate sources of prescribing information.