According to a new study, people who consume herbal supplements may be consuming more than they think.

A new study finds that several herbal products contain ingredients that are not listed on the label. Researchers say that nearly 60 percent of products tested contained plant substances that were not listed on the label, while a third of the products’ main ingredients listed on the label were substituted with a different ingredient. Over 20 percent of the products  had been contaminated with fillers such as wheat, rice, and soybeans in addition to the main ingredient.

Out of the twelve companies tested, only two of the products had no substitutions, contaminants, or fillers. Unlisted ingredients can pose serious health hazards for consumers. Researchers say products contaminated with fillers including walnut leaves, wheat, rice, and soybeans may pose health problems for people with allergies.

During this study, researchers analyzed 44 herbal products sold in the United States and Canada. Herbal products sold in the United States are classified as dietary supplements; however, if found unsafe can be pulled from store shelves.