Protocatechuic acid (PCA) is a dihydroxybenzoic acid, a type of phenolic acid. It is a major metabolite of antioxidant polyphenols found in green tea. It has mixed effects on normal and cancer cells in in vitro and in vivo studies.

Protocatechuic acid (PCA) is antioxidant and anti-inflammatory. PCA extracted from Hibiscus sabdariffa protected against chemically induced liver toxicity in vivo. In vitro testing documented antioxidant and anti-inflammatory activity of PCA, while liver protection in vivo was measured by chemical markers and histological assessment.