T he beta-blocker propranolol has been a mainstay of American medicine since the 1960s, when it was regularly prescribed as a first-line defense against hypertension, arrhythmia, and other cardiovascular problems. Recent years, though, have seen a boom in the medication’s prescription rates—in part because as the drug regulates the heart, it also settles the nerves. Off-label, propranolol is used to calm the assorted storms of stage fright: the sweaty palms, the belly churn, the racing heart.