From the wiki: "By the 1930s, muckraking journalists, consumer protection organizations, and federal regulators began mounting a campaign for stronger regulatory authority by publicizing a list of injurious products which had been ruled permissible under the 1906 law, including radioactive beverages, the mascara Lash lure, which caused blindness, and worthless "cures" for diabetes and tuberculosis. The resulting proposed law was unable to get through Congress for five years, but was rapidly enacted into law following the public outcry over the 1937 Elixir Sulfanilamide tragedy, in which over 100 people died after using a drug formulated with a toxic, untested solvent."

I believe I've heard that the FDA was actually beneficial for capitalism as consumers would entirely avoid certain products out of fear, making it difficult to sell even legitimate goods.