The ragweed decision gets made in a pharmacy aisle in about ninety seconds, somewhere between the box that says non-drowsy and the one with a "D" after the drug name. Three weeks later, the dryness is worse, the sleep is stranger, and the blood pressure has crept up — and nobody has connected those three things to the medication sitting in the middle of them. Here's what each class actually does, and why it lands differently at 49 than it did at 29.