The magnesium citrate powder used in the tablets is sourced from China / USA thought the finished tablets are manufactured here in the UK. The Magnesium Citrate powder is from a fully vetted supplier that has completed a verification process consisting of a meticulous questionnaire and thorough sampling of the material before approval. A technical team, which includes six trained lead auditors, travel to all parts of the world auditing suppliers to ensure products meet all regulatory and quality requirements, and adhere to our environmental and social responsibility policies. All materials received undergo strict quality testing. Batches are sampled, then tested using FTIR analysis and many other methods as required.