Zyrtec is an antihistamine also known as Reactine. Antihistamines are prescribed medicines to treat symptoms of hay fever and other allergic reactions. As its name suggests, antihistamines work by opposing histamines. Histamines are the major causes of itching, sneezing, runny nose, and watery eyes. At times, histamines may cause more than these symptoms; they may block the passage of the lungs which are the bronchial tubes that could make breathing difficult. That is when antihistamines are prescribed to ease up the action caused by histamines and such a drug is Zyrtec.
Zyrtec Indications

Aside from the prevention of allergies, another function of Zyrtec is to inhibit Motion sickness, nausea, vomiting, and dizziness.

Some antihistamines may used to treat chronic uticaria, a persistent rash that looks like hives.

Zyrtec Side Effects

One of the most common side effects of Antihistamines, including Zyrtec is drowsiness. Expect a sleepy feeling when on Zyrtec medication. This effect of Antihistamines is often used to put people to sleep.

In children, serious side effects of Zyrtec might reach up to convulsions in younger patients, unusual irritability as well as unusual excitement and nightmares may likely happen.

In adults, some of the serious side effects may entail difficulty in urination, dizziness, faint feeling, mouth, nose and throat dryness, and also irritability and unusual excitements.
Zyrtec Warnings

Always talk to your doctor first if you have known or unknown allergic reactions to antihistamines and if you have allergies towards foods, preservatives or dyes.

Also take time to inform your doctor about your diet. It is an important consideration that you refer to your doctor if you observe a low fat diet, low protein diet or if you regularly drink alcoholic beverages as they may have an effect on taking Zyrtec.

Pregnancy and Zyrtec have not been studied but drugs that contain cetirizine have not been shown to cause birth defects in pregnant women. However, it has been noticed that certain amounts of antihistamine may be passed on through breast milk. Babies are more prone to catch the side effects of antihistamines and among the side effects are unusual excitements or irritability. The flow of breast milk might also be decreased.

If you are taking sedatives or tranquilizers, never take this medicine without your doctor’s approval.
Zyrtec Reactions

Zyrtec may react with the following medicines, so consult your doctor first if you are taking them or planning to take medicines belonging to the list below:
Anticholinergics
Erythromycin
Ketoconazole – use of this medicine may increase of fexofenadine in the blood
Central Nervous System depressants
Monoamine Oxidase inhibitors – this medicine should never be used together with Zyrtec

When you also have medical problems such as the following:
Enlarged Prostate
Urinary difficulties – Zyrtec may worsen the condition
Glaucoma – Zyrtec may increase eye pressure and worsen the problem
Intestinal Impediments
Stomach Ulcers
Liver Diseases
Kidney Diseases

Consult your doctor for advice on whether to stop your Zyrtec treatment or whether your dosage will be significantly lowered.

What drug(s) may interact with cetirizine?
Because cetirizine can cause drowsiness, other medicines that also cause drowsiness may increase this effect of cetirizine. Some medicines that cause drowsiness are:
•alcohol
•barbiturates such as phenobarbital
•certain antidepressants or tranquilizers (for example, amitriptyline, chlorpromazine, desipramine, doxepin, imipramine, nortriptyline, thioridazine, trifluoperazine)
•certain narcotics or pain medicines (for example, codeine, hydrocodone, meperidine, methadone, morphine, oxycodone, or propoxyphene)
•certain medicines used for anxiety or to help produce sleep (for example, alprazolam, chloral hydrate, diazepam, lorazepam, meprobamate)
•certain antihistamines used in cold medicines (for example, diphenhydramine or chlorpheniramine)
Ask your prescriber or health care professional about other medicines that may increase the effect of cetirizine.

Tell your prescriber or health care professional about all other medicines you are taking, including non-prescription medicines, nutritional supplements, or herbal products. Also tell your prescriber or health care professional if you are a frequent user of drinks with caffeine or alcohol, if you smoke, or if you use illegal drugs. These may affect the way your medicine works. Check with your health care professional before stopping or starting any of your medicines.

What side effects may I notice from taking cetirizine?
Serious side effects to cetirizine are rare. Side effects that you should report to your prescriber or health care professional as soon as possible:
•any unusual effects that are bothersome

Side effects that usually do not require medical attention (report to your prescriber or health care professional if they continue or are bothersome):
•diarrhea
•dizziness
•drowsiness
•dry mouth
•fatigue
•headache
•nausea or stomach upset
•sore throat