An allergy is the inappropriate activation of your immune system to foreign substances, such as pollen, dust and pet dander. Your immune system releases chemical signals to fight infection; however, these chemical signals can be released against harmless substances. According to the Mayo Clinic, allergies can cause symptoms that involve your skin, sinuses, airways or digestive system 1. Fortunately, Zyrtec is available over the counter (OTC) to relieve symptoms of upper respiratory allergies. As with all medications, it is good to be aware of the active ingredients in Zyrtec and their possible side effects.

Cetirizine Actions

According to Zyrtec.com, the active ingredient in Zyrtec is cetirizine. Cetirizine works by blocking the receptors of chemical signals that cause upper respiratory symptoms. During an allergic reaction, your body’s immune system releases histamines that causes sneezing, itching, stuffy or runny nose, cough or sinus headaches. Cetirizine blocks the action of histamines on your body. This ingredient is most effective when taken before exposure to an allergen. Therefore, try to take cetirizine before being exposed to substances that you are allergic to. Important side effects of this active ingredient include drowsiness, dry mouth and fatigue, according to Drugs.com. In children, Drugs.com also states that cetirizine can cause:

• abdominal pain
  
• coughing
  
• diarrhea
  
• headache
  
• nosebleed
  
• sleepiness
  
• sore throat
  
• wheezing

Let your doctor know if you are having any side effects from this medication. In addition, let your doctor know if cetirizine is not controlling your symptoms.

Croscarmellose Sodium

Inactive ingredients, or excipients, are substances that support the active ingredient or help with ease of use of the medication. For example, croscarmellose sodium is an inactive ingredient used in Zyrtec, according to Zyrtec.com. According to the journal "Pharmaceutical Development and Technology," croscarmellose sodium is a substance added to Zyrtec to help the tablet properly break down in the digestive tract. Without this ingredient, the tablet may not dissolve or may dissolve in an improper location. This can reduce the effectiveness of this medication.

Inactive Ingredients

Consult your doctor before taking Zyrtec if you are allergic to any of these inactive ingredients.