After Sinclair brings attention to unhygienic conditions in the Chicago stockyards, the Pure Food and Drug Act is passed. It is also known as the "Wiley Act," referencing Harvey Washington Wiley, the chief chemist of the U.S. Department of Agriculture at the time.

The act focuses on accurate product labeling, and outlaws interstate trade in “adulterated” and “misbranded” foods. It requires producers to indicate the presence of mixtures and/or impurities on product labels. This is the first time this regulation is applied to cosmetics and pharmaceuticals as well as food. Responsibility for enforcement moves from the Board of Food and Drug Inspection to the Bureau of Chemistry.

The act also includes cannabis among the various substances that patent medicine companies are required to list on their labels so that worried customers can avoid it. It becomes the first of a series of consumer protection laws that are enacted by Congress in the early 20th century.