Rosmarinic acid is a widespread phenolic ester compound in the plants. Rosmarinic acid inhibits MAO-A, MAO-B and COMT enzymes with IC₅₀s of 50.1, 184.6 and 26.7 μM, respectively. IC50 & Target: IC50: 50.1 μM (MAO-A), 184.6 μM (MAO-B), 26.7 μM (COMT)^[1] In Vitro: Rosmarinic acid (RA) shows an in vitro multifunctional profile characterized by antioxidant effects, and monoamine oxidases (MAO-A and MAO-B) and catechol-O-methyl transferase (COMT) inhibition. Rosmarinic acid shows antioxidant effects against hydroxyl (HO(•)) and nitric oxide (NO) radicals (IC₅₀ of 29.4 and 140 μM, respectively), and inhibition of lipid peroxidation (IC₅₀ of 19.6 μM)^[1]. Rosmarinic acid (RA) exerts a significant cytoprotective effect by scavenging intracellular ROS induced by UVB. In H₂O₂-treated cells, 2.5 μM Rosmarinic acid scavenges 60% of intracellular ROS compared to 77% of intracellular ROS scavenging effect in N-acetyl-L-cysteine (NAC)^[2]. In Vivo: Rosmarinic acid (RA) is a widespread phenolic ester compound in the plants, particularly those in the Labiatae family of herbs, such as Rosmarinus officinali, Salvia miltiorrhiza, and Prunella vulgaris. Rosmarinic acid suppresses colonic inflammation in dextran sulphate sodium (DSS)-induced mice via dual inhibition of NF-κB and STAT3 activation. In the DSS-induced colitis model, Treatment with Rosmarinic acid (30, 60 mg/kg, p.o.) markedly attenuates the production of cytokines^[3].