I've been taking certrizine for the past 14 years for my urticaria and anaphylaxis. What is the worst side effect that could happen?

Zyrtec (cetirizine) Always read the bottle for long term side effects some of which can be headaches (too dry sinuses), weakened urinary stream (more common in men with big prostates), abdominal pain, dry mouth.
Urinary retention. Cetirizine is the activated form of Hydroxyzine (atarax). Hydroxyzine has been in use for over 60 years. We know there are no long-term chronic adverse effects. After taking this medication for 14 years drowsiness, prolonged reaction time, or dry mucous membranes are not likely going to bother you. As you get older constipation for anyone & difficulty urinating for men are more likely to occur.