Carnosic acid, a major polyphenolic diterpene found in rosemary (Rosmarinus officinalis), has been investigated in preclinical studies for its potential to support or treat non-alcoholic fatty liver disease (NAFLD) and related liver conditions. Scientific interest is based on its antioxidative, anti-inflammatory, and lipid-lowering properties. Several in vitro and animal studies have demonstrated that carnosic acid can attenuate hepatic steatosis, reduce oxidative stress, and modulate lipid metabolism pathways in models of fatty liver disease. For example, research in rodent models has shown that carnosic acid supplementation can decrease hepatic lipid accumulation, suppress inflammatory cytokines, and improve markers of liver function.

Mechanistically, carnosic acid appears to activate AMP-activated protein kinase (AMPK) and inhibit the expression of key lipogenic genes, reducing triglyceride synthesis in the liver. It may also enhance antioxidant defenses by upregulating the Nrf2 pathway. However, to date, these effects have only been demonstrated in laboratory and animal models; there are no published human clinical trials directly assessing carnosic acid supplementation for NAFLD or fatty liver disease. As such, while the mechanistic and preclinical evidence is promising, clinical validation is lacking. The overall quality of evidence is therefore rated as low to moderate (2/5), pending future human research.