New FDA-approved drugs to treat hepatitis C have been incredibly expensive but also kind of miraculous. They actually cure the disease, which untreated can cause liver disease and cancer.

But now the FDA is warning of potentially life-threatening complications from some of these drugs—at least 26 people taking either Viekira Pak or Technivie, both made by AbbVie, have had a severe, atypical worsening of their already existing liver disease. In some cases, the damage led to the need for liver transplantation or to death. If you’re taking one of these medications—or know someone who is—talk to your doctor right away.

Most of the patients affected already had advanced cirrhosis (scarring of the liver), and several people had other medical conditions that were contraindications—meaning that they shouldn’t have been taking the medications in the first place.

But the terrible results for these patients raises serious doubt about a common insurance practice—denying these medications to people with hepatitis C that hasn’t yet caused liver disease. Waiting until people with hepatitis C actually have advanced liver damage before agreeing to pay for these drugs is a penny-pinching policy that may be putting patients in harm’s way.