Grazoprevir is a drug[1] approved for the treatment of hepatitis C. It was developed by Merck and completed Phase III trials, used in combination with the NS5A replication complex inhibitor elbasvir under the trade name Zepatier, either with or without ribavirin.

[3] It has good activity against a range of HCV genotype variants, including some that are resistant to most currently used antiviral medications.

Common side effects of the combination include feeling tired, nausea, reduced appetite, and headache.

Drugs that inhibit this proteins, such as rifampicin, ciclosporin, and a number of AIDS medications (atazanavir, darunavir, lopinavir, saquinavir, tipranavir, cobicistat), can cause a significant increase in grazoprevir blood plasma levels.

Combination with drugs that induce this enzyme, such as efavirenz, carbamazepine or St. John's wort, can lead to ineffectively low plasma levels of grazoprevir.