MSM is an excellent dietary source of bioavailable organic sulfur. Doctor's Best MSM features OptiMSM, a highly purified form (99.9% pure) of methylsulfonylmethane (MSM). Since the amount of MSM found naturally in living materials is too small to be extracted, the MSM used for dietary supplements is manufactured. The makers of OptiMSM developed a four-stage process to separate impurities including heavy metals and other contaminants from OptiMSM. Each batch exceeds the United States Pharmacopeia (USP) monograph standards for MSM, and is validated by testing in independent laboratories.