Clarinex-D 12 hour is a prescription allergy medicine that contains an antihistamine and sudafed to control seasonal allergies. I never had allergies until I moved to Texas 11 years ago but 9 months after I moved here my allergies were so severe they interfered with my life. After undergoing allergy testing (skin test) I discovered I'm allergic to pretty much everything that grows here. Fiveyears of allergy shots did little to help. Then I was put on Clarinex-D 12 hour and my life changed! I've been taking it for about 4 years now and rarely do I have a day where I feel like I have horrible allergies. It is a 12 hour pill but I only take one in the morning because of the sudafed. (I don't want it to keep my up all night) Even when everone around me is complaining that their allergies are horrible I'm okay because I take my Clarinex-D 12 hour EVERY DAY! It's pretty expensive but to me it's worth it to not have to worry about my allergies all the time. If you suffer from seasonal allergies I recommend talking to your doctor about Clarinex-D 12hr to see if it's right for you!