Rhein is an anthraquinone derivative that has been found in R. rhabarbarum and is an active metabolite of diacerein that has diverse biological activities, including anticancer, antioxidant, and anti-inflammatory activities.^1,2,3,4 It induces cell cycle arrest at the S phase and inhibits the proliferation of HepG2 cells when used at concentrations of 40 and 100 µM, respectively.¹ Rhein (100 and 200 µM) also inhibits proliferation of MCF-7 and MDA-MB-435s breast cancer cells under normoxic and hypoxic conditions.² It reduces controlled cortical impact-induced decreases in catalase and superoxide dismutase (SOD) activity and malondialdehyde (MDA), glutathione, and glutathione disulfide levels in the brain in a rat model of traumatic brain injury when administered at a dose of 12 mg/kg.³ Rhein (50 mg/kg per day) reduces cerulein-induced increases in serum TNF-α, IL-1β, and amylase levels, as well as reduces pancreatic glandular atrophy and fibrosis, in a mouse model of chronic pancreatitis.⁴