1. Pharmaceutical grade. This grade meets highest regulatory requirements for purity, dissolution, and absorption and is designated by "USP 23" or says "standardized" or "extract."
2. Medical grade. This is a high-grade product. Prenatal vitamins usually fit into this category.
3. Cosmetic, nutritional grade. Supplements of this grade are usually sold in health food stores. These often are not tested for purity, dissolution, or absorption and may not have a high concentration of the active ingredient they are labeled as.
4. Feed or agricultural grade. Supplements of this grade are used for veterinary purposes. Do not use supplements of this grade.