Before you have any skin tests for allergies, tell the doctor in charge that you are taking ZYRTEC. The results of the test may be affected by ZYRTEC.

When taking antihistamines on a regular basis, make sure your doctor knows if you are taking large amounts of aspirin at the same time (as for arthritis or rheumatism). Effects of too much aspirin, such as ringing in the ears, may be covered up by the antihistamine.

Antihistamines will add to the effects of alcohol and other CNS depressants (medicines that slow down the nervous system, possibly causing drowsiness). Some examples of CNS depressants are sedatives, tranquilizers, or sleeping medicine; prescription pain medicine or narcotics; barbiturates; medicine for seizures; muscle relaxants; or anesthetics, including some dental anesthetics. Check with your doctor before taking any of the above while you are using ZYRTEC.

ZYRTEC may cause some people to become drowsy or less alert than they are normally. Even if taken at bedtime, it may cause some people to feel drowsy or less alert on arising. Some antihistamines are more likely to cause drowsiness than others. Drowsiness is less likely with cetirizine, and rare with desloratadine and loratadine. Make sure you know how you react to the antihistamine you are taking before you drive, use machines, or do anything else that could be dangerous if you are not alert.

Antihistamines may cause dryness of the mouth, nose, and throat. Some antihistamines are more likely to cause dryness of the mouth than others . For temporary relief of mouth dryness, use sugarless candy or gum, melt bits of ice in your mouth, or use a saliva substitute. However, if your mouth continues to feel dry for more than 2 weeks, check with your medical doctor or dentist. Continuing dryness of the mouth may increase the chance of dental disease, including tooth decay, gum disease, and fungus infections.

For patients using dimenhydrinate, diphenhydramine, or hydroxyzine:

• ZYRTEC controls nausea and vomiting. For this reason, it may cover up the signs of overdose caused by other medicines or the symptoms of appendicitis. This will make it difficult for your doctor to diagnose these conditions. Make sure your doctor knows that you are taking ZYRTEC if you have other symptoms of appendicitis such as stomach or lower abdominal pain, cramping, or soreness. Also, if you think you may have taken an overdose of any medicine, tell your doctor that you are taking ZYRTEC.

For patients using diphenhydramine or doxylamine as a sleeping aid:

• If you are already taking a sedative or tranquilizer, do not take ZYRTEC without consulting your doctor first.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if the following side effect occurs:

• Less common or rare

  Less frequent or rare with azatadine, cetirizine, clemastine, cyproheptadine, desloratadine, dexchlorpheniramine, diphenhydramine, or loratadine

  • Fast or irregular heartbeat;  fever;  abdominal or stomach pain;  burning;  chills;  clay-colored stools or dark urine;  cough;  diarrhea;  difficulty swallowing;  dizziness;  fast heartbeat;  fever;  headache;  hives;  itching;  prickly sensations;  puffiness or swelling of the eyelids or around the eyes, face, lips or tongue ;  redness of skin;  seizures ;  shortness of breath;  skin rash;  swelling;  tightness in chest;  tingling;  unusual tiredness or weakness;  wheezing 
  
  

Also, check with your doctor as soon as possible if any of the following side effects occur:

• Less common or rare
  • Sore throat;  unusual bleeding or bruising ;  unusual tiredness or weakness 
  
  

• Symptoms of overdose
  • Clumsiness or unsteadiness;  convulsions (seizures);  drowsiness (severe);  dryness of mouth, nose, or throat (severe);  feeling faint;  flushing or redness of face;  hallucinations (seeing, hearing, or feeling things that are not there);  shortness of breath or troubled breathing ;  trouble in sleeping 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your health care professional if any of the following side effects continue or are bothersome:

• More common
  • Drowsiness;  dry mouth, nose, or throat ;  gastrointestinal upset, stomach pain, or nausea ;  headache;  increased appetite and weight gain;  thickening of mucus 
  
  

• Less common or rare
  • Acid or sour stomach;  belching;  blurred vision or any change in vision;  clumsiness or unsteadiness;  body aches or pain;  confusion (not with diphenhydramine);  congestion;  constipation;  cough;  diarrhea;  difficult or painful urination;  difficulty in moving;  difficult or painful menstruation;  dizziness (not with brompheniramine or hydroxyzine;  drowsiness (with high doses of desloratadine and loratadine);  dryness of mouth, nose, or throat;  early menstruation;  fast heartbeat;  fatigue;  fever;  gastrointestinal upset, stomach pain or nausea;  heartburn;  hoarseness;  increased appetite and weight gain;  increased sensitivity of skin to sun;  increased sweating;  indigestion;  loss of appetite;  joint pain;  muscle aching or cramping ;  muscle pains or stiffness;  nausea;  nightmares (not with azatadine, chlorpheniramine, cyproheptadine, desloratadine, hydroxyzine, or loratadine);  ringing or buzzing in ears;  runny nose;  skin rash;  swollen joints;  stomach discomfort, upset or pain;  tender swollen glands in neck;  thickening of mucus ;  tremor;  unusual excitement, nervousness, restlessness, or irritability;  vomiting  
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your health care professional.

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although this use is not included in product labeling, cetirizine and loratadine are used in certain patients with asthma together with asthma medicines. The antihistamine is used before and during exposure to substances that cause reactions, to prevent or reduce bronchospasm (wheezing or difficulty in breathing).

Cyproheptadine is used as an appetite stimulant, in adults and children

Cyproheptadine is used for treatment of vascular headaches.

Other than the above information, there is no additional information relating to proper use, precautions, or side effects for this use.