In the 1950s, Obetrol was manufactured by Obetrol Pharmaceuticals, in Brooklyn, New York. The company later became a division of Rexar Pharmacal Corporation, which was also headquartered in Brooklyn. Sometime prior to 1972, Rexar Pharmacal moved its manufacturing facilities, including its Obetrol Pharmaceutical Division, to Valley Stream, New York. By the 1990s, Obetrol Pharmaceuticals had been wholly absorbed by Rexar Pharmacal and was no longer noted as a "division" of Rexar. In 1993, Rexar was acquired by Richwood Pharmaceuticals of Florence, Kentucky, which in 1995 merged with Shire Pharmaceuticals.