Circadian rhythms are crucial for liver homeostasis. In an in vitro liver system, primary human hepatocytes showed 24-hour oscillations, revealing dynamic gene expression related to inflammation, drug metabolism, and energy homeostasis. A treatment protocol was developed to reduce hepatotoxicity from atorvastatin and acetaminophen. Additionally, circadian phases significantly influenced pro-inflammatory cytokine induction in response to infections, highlighting their impact on drug efficacy and toxicity.