I'm a 21 year old male and I have had seasonal allergies throughout my life. Before this year, I had been taking allergy medication and Zyrtec did the job
and I was never miserable. Since my allergies started acting up this season, I've been taking Zyrtec once a day consistently. It helps for the first 6 to 8 hours, and then after that I'm miserable again: sneeze attacks, runny nose, watering eyes to the point of not being able to see very well, and coughing.
Zyrtec is pretty strong stuff.