N wasn’t expecting drama on a routine visit to the eye doctor. But fortunately her doctor had a lifesaving insight for both her and her sister, K: “I think you have Wilson’s disease,” he told N after noticing strange golden-brown rings in her irises.

Wilson’s is a rare inherited disorder—only one in about 30,000 people worldwide has it—in which the body can’t metabolize copper. Untreated, it can lead to fluid buildup, jaundice, neurological issues, and fatal liver failure. There was no surefire treatment until the mid-1950s, when a British doctor discovered two drugs that now go under the trade names Cuprimine and Syprine. Today these are the standard treatments for Wilson’s, and they must be taken for life.

The sisters began taking Syprine in 1987. Their symptoms went away, and they both went on to highly successful careers, N as a public-relations executive and K in the wealth-management division of a major investment firm. Their insurance covered the cost of the drug, which wasn’t much because Syprine is simple to make. The sisters were vaguely aware that, in the latter part of the aughts, their co-pays, originally next to nothing, had started to climb, but health insurance still insulated them from the realities of drug pricing.

That is, until it didn’t, in 2014, when N went to her local Walgreens to pick up her lifesaving supply of Syprine—and found that her insurance company had denied coverage on the grounds that the drug was too expensive. Shocked, she asked the pharmacist the cost. She remembers him saying it had risen to around $20,000 for a month’s supply. She eventually managed to get coverage—after all, treating her for liver failure would have been more expensive—but the co-pays have continued to climb. She and K now pay $500 and $400, respectively, for a three-month supply.

Syprine, which can be had for $1 a pill in some countries, now has a list price of around $300,000 for a year’s supply in the United States; Cuprimine has seen a similar price increase. There is no generic version of either, in part because of a huge backlog for new drug approvals at the F.D.A.

Both sisters have done well financially, but their health insurance in retirement is uncertain, and they are terrified about the consequences if their co-pays eventually get calculated as a percentage of a drug’s total cost, the likelihood of which is “1,000 percent,” according to Art Caplan, the head of the medical-ethics division at New York University. “I have advantages, but I can’t fix this,” says K. “You are at the mercy of this abhorrent system.”

N’s husband, J, began investigating the impenetrable “hot mess”—as Caplan calls it—of how drugs get priced in the U.S. He found that, in 2006, Merck, which had originally owned Cuprimine and Syprine, sold the drugs to a small company called Aton, which began raising the prices. Then, in 2010, Aton sold the drugs to Valeant Pharmaceuticals.

In 2014, J read an article in The Wall Street Journal about Valeant and its C.E.O., 55-year-old Michael Pearson, and the reasons for the outrageous price increases of his wife’s medicine became clearer. “Supporters say Mr. Pearson’s approach should be a blueprint for the pharmaceutical industry’s future: Grow through serial deal-making, including tax ‘inversion’ purchases of foreign companies to take advantage of lower tax rates [abroad]. Cut costs aggressively. And, above all, stop spending so much money on risky research,” wrote the Journal. The article quoted Mason Morfit, the president of ValueAct Capital, a prominent investment fund, saying that Pearson “is the best CEO I’ve ever worked with.”

J learned that Valeant had bought Aton, for $318 million in 2010. In presentations Pearson bragged to investors that the purchase had quickly earned back 2.5 times its cost. Though the patient base for Syprine is tiny, the drug, thanks to its exorbitant price hikes, had become one of Valeant’s top-20 drugs by revenue by 2014. “I realized these guys were going to raise prices however much they wanted with no consequences,” J says.