Over-the-counter allergy relief medications Zyrtec and Claritin have similar effects but different groups of people react adversely to them. For example, if you use muscle relaxants, sleeping pills or other allergy medications, Zyrtec is not advisable. People suffering from liver disorders or PKU (phenylketonuria) should avoid Claritin. But Zyrtec and Claritin are both by and large equally effective as antihistamines i.e. in alleviating allergy symptoms. Zyrtec and Claritin both provide relief from hay fever (allergic rhinitis), urticaria (hives), angioedema and other skin allergies. It also treats allergic reactions like sneezing, runny nose, itchy or burning eyes. It may also be prescribed for treating mild to moderate headaches.
The effect of Claritin peaks in 1–2 hours. Its half-life is 8 hours. Traces of Claritin remain in the body for approximately 28 hours. 40% is excreted as conjugated metabolites into the urine, and a similar amount is excreted into the feces. Traces of unmetabolised loratadine can be found in the urine.
The effects of Zyrtec start within about an hour. Zyrtec remains in the body for a maximum of 21 hours. Its half-life is 8.3 hours. 70% of the drug is removed through urination, of which half is observed as unchanged cetirizine compound. Another 10% is excreted.
With all drugs there will be side effects and you have to decide which side effects you can tolerate while enjoying the benefits of the medication. I choose Zyrtec as my favorite because it did not cause as much dryness as Claritin did. For me I could handle the drowsiness of Zyrtec over Claritin's dryness. Both medications are equally effective and will effect each person differently.