I know this response is late, but I just thought I'd let you know that my Mom suffers from HORRIBLE allergies and she tried Zyrtec but it wouldn't last a complete 24 hour cycle for her so she asked her doctor and he told her that sometimes a store-brand of the same medicine can work differently (their formulas can be slightly different) and he recommended that she try that route...and so she did. She decided to start out with Walgreen's brand of Zyrtec and she couldn't believe the difference---it worked a whole 24-hour cycle for her and she is really happy with it. Plus, she was even more happy that it cost a lot less than the Zyrtec brand. So, I just thought I'd let you know this in case the Zyrtec doesn't work the full cycle for you. Allergies stink! I sure hope you find relief!
By the way...she takes it first thing in the morning so that by the time she gets ready for work and drives to work it has started working. But, it works differently for everyone so you'll need to find what works best for you. ~Kimberly