Generics are no longer rock-bottom bargains. The New York Times reports that doctors are finding that prices associated with drugs once considered cheap—such as the heart drug digoxin which has been around since 1785—are rising because drugmakers have little incentive to do otherwise.

The Times notes that the companies which make the drug have doubled its price since last year, and that patients are now laying out anywhere from $50 to $1,000 a year for the generic. One patient tells the Times her monthly co-pay for the drug rose from $1.15 for a three-month supply, to $90, taking a significant bite out of her $1,600-a-month income.

Harvard School of Public Health’s professor of economics Aaron Kesselheim tells the Times that generics are cheap once four or five competitors have to share a market. The Times notes that two companies dominate the generic digoxin market and a third company started producing an authorized generic in January. The Times notes authorized generics tend to be pricier than other generics because they use the branded drug’s formula.

NYT notes that this price-raising scenario is happening with a number of pharmaceuticals, including generic Fiorinal with codeine for migraines and generic thyroid medication Synthroid.