What is Zyrtec®?
Zyrtec® tablets are an anti-allergy remedy containing the active ingredient Cetirizine Hydrochloride 10mg. The most common form of allergy is hayfever, a seasonal disorder occurring during Spring and Summer caused by airborne pollens. Typical symptoms include sneezing, runny nose and itchy watery eyes. Other allergies are caused by eating certain foods, through contact with certain drugs or chemicals, or those caused by house dust mites or animal fur. These reactions are caused by an allergic reaction between the allergen and certain cells in the body. This reaction triggers the release of a number of chemical substances which irritate the body. One of these chemicals is histamine. There are a number of medicines available for treating allergies, the most common being antihistamines. Some antihistamines also counteract the effects of other irritating chemical substances as well as those of histamine. These are called anti-allergics. 
Zyrtec® is an anti-allergic used to treat heyfever and other allergic reactions. It is fast acting (10-20 minutes) non-sedating and lasts for 24 hours. For children under 12 years, twice daily dosage is recommended because the effect of Zyrtec® does not last as long in children. 
Use: 
Cetirizine or Zyrtec® is a non-sedating antihistamine. It is a metabolite of hydroxyzine, an sedating antihistamine. 

How It Works: 
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. 

Side Effects: 
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. 

Cautions for People: 
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. 

Drug Interactions: 
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. 

Before taking Zyrtec: 
Pregnant or breast feeding women should consult a doctor before taking Zyrtec®. People with known hypersensitivity to Zyrtec® should AVOID taking it. People with kidney problems should seek medical advice before taking Zyrtec®, a smaller dose may be necessary.