A temporary elevation of of liver function enzymes such as the aminotransferase levels (ALT and AST) and alkaline phosphatase (ALP) have been reported in some patients using CHANTIX with underlying liver disease such as alcoholic liver disease and/or hepatitis virus infections. These elevations are usually noticed after one month of treatment with Chantix (varenicline) and once the drug is stopped the levels return to baseline levels within a few months. Therefore for patients with impaired hepatic function following liver functions with routine blood test is warranted.
So if you drink a lot or if you know you have chronic hepatitis you should make sure to let your doctor know prior to starting on Chantix.
Source: Acute Hepatic Injury Associated with Varenicline in a Patient with Underlying Liver Disease. The Annals of Pharmacotherapy: Vol. 43, No. 9, pp. 1539-1543.