Cesium chloride (CsCl) is an inorganic salt promoted as an alternative cancer therapy and available for purchase as a dietary supplement in the United States. Cesium is an alkali metal whose radioisotope (Cesium 137) is used in radiation therapy, but the radioactive form can easily contaminate the environment. Cesium chloride, a non-radioactive salt, is used as an alternative cancer treatment based on the affinity of cancer cells for cesium ions, also known as ‘high pH therapy’. Its mechanism of action is to increase the intracellular pH of tumour cells to exert an anti-tumour effect. The resulting alkaline environment is thought to prevent cancer cells from undergoing mitosis, which ultimately leads to cell death.

However, the FDA has not approved CsCl products for the treatment of cancer or other diseases. In addition, studies have shown that taking CsCl orally or by injection can cause serious heart problems related to low blood levels of potassium, a mineral that is essential for proper heart function. Adverse reactions in some cancer patients treated with CsCl have included: prolonged QT intervals, cardiac arrhythmia, fainting, low potassium levels, urinary potassium depletion, seizures, and death.  

The use of caesium poses significant safety risks (e.g., cardiotoxicity) and may be associated with death.The FDA classifies caesium chloride as an ‘API’, a category of substances that pose significant safety risks in combination drugs. It also issued a warning to avoid dietary supplements containing cesium chloride or any other cesium salt.