Users of the popular allergy drug can experience withdrawal symptoms. I was one of them. — Katie DeRosa, a 26-year-old graphic designer in Lawrence, Massachusetts, went to see her allergy doctor in 2014 about a nagging post-nasal drip. The doctor suggested she try the popular over-the-counter antihistamine Zyrtec, which she started taking regularly. Four years later, DeRosa tried to stop taking the medication. …