Studies conducted in several experimental tumor models in the 1980s found that the use of cesium or cesium chloride led to decreased tumor growth and fewer deaths in certain mice with cancerous tumors, such as those with sarcoma or breast cancer. In animal studies, giving cesium over the long term caused serious blood and neuromuscular side effects and even death. Cesium chloride is sold as a dietary supplement in the United States. Newer reports have suggested that it can take weeks or even months for cesium to cause some of the more severe heart problems.