I have been on Zyrtec for at least 4 yrs and I have to stop to have some allergy test done again.I am 53 yrs old and asthmatic. I have to be off them for 7 days prior to the tests. I can't believe the withdrawal I am getting. I am itching all over and feel as though I am crawling out of my skin. I will take the shots for my allergies and never go back to Zyrtec again. Works great for allergies but don't try to get off them.