4-Aminosalicylic acid (para-aminosalicylic acid or PAS) is an antibiotic used to treat tuberculosis. This organic compound has also been use since the 1940s for the treatment of inflammatory bowel diseases (IBDs), where it has shown greater potency in ulcerative colitis and Crohn's disease. It is thought to act via NF-κB (nuclear factor-kappa B) inhibition and free radical scavenging. The closely related chemical compound 5-aminosalicylic acid, sold under the name mesalazine, also has medical uses.