Per the US FDA package insert for Zyrtec (cetirizine hcl) 10mg tablets: adults and children 12 years and older should not take more than the 24hr recommended maximum dose of 10mg. Helpful answers from trusted Doctors on causes, diagnosis, symptoms, treatment, and more: Dr. Zacharisen delves into whether or not you should take Allegra and Zyrtec together for symptom relief. Relieves your worst allergy symptoms, indoors and out. Get allergy relief that starts working faster than Claritin® on the first day you take it.* Zyrtec perhaps was recommended by your doc to be taken in the night as it causes drowsiness to around 13-14% people taking this med, it could also cause in about 5-6% people who take Fatigue as its side effects. I started taking Zyrtec for seasonal allergies. After a month on this drug, I noticed a lump on my forehead. I initially dismissed it as acne. But it grew rapidly. On Jul 28, 2000. Yes my kids have been on zyrtec under the age of two.as far as dosage I can't remember. All three take 10 mg. of it daily now, they used to take 5, but due to their high grass allergy they need a higher dosage of the 10 mg. Horrible recommendation. Do not take extra doses of the antihistamine if you've already experienced terrible effects of withdrawal. You are in the 1% of the population that likely experiences these effects, but they won't go away -- you'll be addicted to Zyrtec for life. For Allergic Rhinitis Three years ago I started taking Zyrtec for nasal allergies that included sneezing and stuffy nose. I was previously on Claratin, but it wasn't giving me all day relief, so the doc switched me to Zyrtec. Read about the differences among three common over-the-counter antihistamines, Claritin, Allegra, and Zyrtec, and which one may be right for you. I think Zyrtec is blocking it off as much as it can. I was thinking about taking flonase, I did some research and what I found out was that it's a steriod.