Levocetirizine
"I have used a lot of different allergy medicines (for dust/mold/pollen) and I have never gotten a side-effect as bad I got from this. I switched from Zyrtec to this because of a discount that was given; I have been on it for close to 10 months and then I started losing my short-term memory, lose creativity, and it even started to make me slur words. I don't blame it entirely on this medicine, it MAY have been the combination of this and Astepro; but in my experience this definitely causes drowsiness. I can't completely say to stay away from it just be sure to monitor it right away and after about 5 months. I switched to Allegra 180mg. Hope this helps."