This medication is used to treat rheumatoid arthritis, Wilson's disease (a condition in which high levels of copper in the body cause damage to the liver, brain, and other organs), and a certain disorder which causes kidney stones (cystinuria). For the treatment of rheumatoid arthritis, penicillamine is known as a disease-modifying antirheumatic drug (DMARD). It helps to decrease pain/tenderness/swelling in the joints. For the treatment of Wilson's disease, penicillamine binds to copper and helps it to be removed from the body. Decreasing copper levels helps to improve liver function and the mental/mood/nerve problems (such as confusion, difficulty speaking/walking) caused by the disease. For the treatment of cystinuria, penicillamine helps to decrease the amount of a certain substance (cystine) in the urine which can cause kidney stones.