Zyrtec is safe to take with Type 1 diabetes. It does not affect your blood sugar levels. Zyrtec D however should be used with caution in diabetics. Zyrtec (cetirizine) is an antihistamine that reduces the effects of natural chemical histamine in the body. Histamine can produce symptoms of sneezing, itching, watery eyes, and runny nose. What is Zyrtec? Cetirizine is the generic name for the brand name Zyrtec and is a medication that is used to treat moderate to severe allergies, cold symptoms or chronic hives. Adults and children 6 years and over: One 10 mg tablet once daily; do not take more than one 10 mg tablet in 24 hours. A 5 mg product may be appropriate for less severe symptoms. Find answers to frequently asked questions about the different ZYRTEC® allergy products, as well as information about indoor and outdoor allergies. Adults and children 6 years and over should take one 10 mg capsule once daily; do not take more than one 10 mg capsule in 24 hours. A 5 mg product may be appropriate for less severe symptoms. Cetirizine comes as a tablet, a chewable tablet, an extended release tablet, and a syrup (liquid) to take by mouth. It is usually taken once a day with or without food. It's common for people with hives (called urticaria) or hay fever (called allergic rhinitis) to wonder which over-the-counter antihistamine they should take: Claritin (loratadine), Zyrtec (cetirizine), or Allegra (fexofenadine)? I continued taking Zyrtec for the next few years thankful for the relief. But it was not until recently that I began to research my symptoms again because it seemed to only be getting worse. Zyrtec is the brand name of cetirizine, an over-the-counter (OTC) antihistamine used to treat cold and allergy symptoms such as sneezing, itching, watery eyes, or runny nose.