The introduction of Cystic Fibrosis Trans Regulatory modulator (CFTRm) drugs has seen a transformation in Cystic Fibrosis (CF) treatment. This has led to a significant improvement in lung function and quality of life with the potential for a real impact on life expectancy. Transient mild to moderate hepatic transaminitis is a well-known side effect of CFTRm drugs, which often improves on cessation and may not recur following the re-institution of the drug. We describe a case of transaminitis developing nine months after the initiation of Kaftrio, which progressed to liver necrosis despite stopping Kaftrio and took many months to resolve. The patient had experienced significant improvement in lung function and overall health while on Kaftrio and deteriorated when it was stopped. He was keen to restart; however, Kaftrio was not reinstated due to the potential risk of acute liver failure.