Federal health officials are cautioning patients and clinicians about the potential for life-threatening liver injury in two AbbVie drugs used for the treatment of advanced forms of hepatitis C.

The Food and Drug Administration (FDA) announced on Oct. 22, 2015, that AbbVie will need to add new indications to Technivie and Viekira Pak after reported liver transplants and deaths of patients who previously had liver injury caused by the hepatitis C virus. This new indications could restructure the emergent field of high-priced medications for hepatitis C, which also comprises Gilead Sciences’ best-selling drugs Harvoni and Sovaldi, according to a news release.

Brian Abrahams, a Jefferies analyst, mentioned in an investment note that the caution is of a “moderate positive” level for Gilead Sciences, and would further challenge AbbVie’s Viekira Pak, already under pressure because of a similar drug from Merck & Co. that is expected to be approved in 2016.

Tim Anderson, an analyst at Bernstein, also noted that’s AbbVie’s hepatitis C medication requires four to six pills each day, as opposed to the once-daily regiment for Gilead’s Harvoni as well as Merck’s awaited medication. “In the ultra-competitive hep C market, this is likely a damaging event,” Anderson wrote in an investment note.

Approximately 3 million people in the U.S. have hepatitis C, a slow progression virus that, if left untreated, can lead to liver cancer and liver failure. In an online post, the FDA noted that AbbVie’s drugs have been associated with multiple cases of liver damage, some of which led to death, in hepatitis C patients already with liver cirrhosis or permanent scarring of the liver. The agency determined that 26 of these events were likely results of the medications, with  liver damage occurring within four weeks of treatment initiation.

AbbVie stated that a warning will be added to the medications noting they must not be used in patients with moderate to severe liver damage. “Patient safety is of the utmost concern to AbbVie,” the company stated.

AbbVie’s medications belong to a new group of pill-only combined treatments shown to be more effective in treating hepatitis C and generally cause fewer side effects than previous medications, given by injection and known to cause flu-like symptoms. Viekira Pak treats the most common hepatitis C type (genotype 1), accounting for nearly 75% of all hepatitis C cases in the United States. Technivie, approved in July, was developed to treat one of the least common forms of hepatitis C.

Gilead Sciences initially controlled the market, reporting $9.4 billion in sales for its Sovaldi medication during its first year on the market. The drug was approved by the FDA in December 2013. Gilead followed that approval with the introduction of Harvoni, a combination pill for the treatment of a broader group of patients with hepatitis C.

While patients and clinicians have embraced the new medications, insurers are troubled by their high prices — about $83,000 for one treatment course. The introduction of AbbVie’s Viekira Pak was embraced as a much-needed competitor in the field.