The blockbuster hepatitis C drug Sovaldi has generated a staggering $5.7 billion in sales over the first half of 2014, according to an earnings report on Wednesday from Gilead Sciences. The medicine has attracted attention both for its effectiveness—it helps cure the deadly liver disease in 90 percent of patients—and its $84,000 price for a three-month course of treatment. Gilead noted on its earnings call that it believes 9,000 people have been cured so far. Sovaldi isn't the first high-priced drug, but its potential population of patients is huge: Three million Americans are estimated to have hepatitis C, although many are asymptomatic and unaware they're infected.