https://dietarysupplementdatabase.usda.nih.gov/

The Dietary Supplement Ingredient Database (DSID) provides estimated levels of ingredients in dietary supplement products sold in the United States. These estimates, which are based on chemical analysis of nationally representative products, may differ from the labeled amounts. The DSID offers data for understanding the actual content of dietary supplements, supporting research, regulation, and consumer awareness regarding the accuracy and quality of supplement ingredients.