S-Methylisothiourea sulfate is primarily used as a reagent in organic synthesis, particularly in the preparation of guanidine derivatives. These derivatives are valuable in the development of pharmaceuticals, including drugs that target cardiovascular diseases and hypertension. It is also employed in biochemical research as a selective inhibitor of nitric oxide synthase, aiding in the study of nitric oxide's role in various physiological and pathological processes. Additionally, this compound finds application in the synthesis of agrochemicals, contributing to the production of pesticides and herbicides that enhance crop protection. Its versatility in chemical reactions makes it a useful intermediate in industrial and laboratory settings.