 The Kefauver Harris Amendment strengthened the U.S. Food and Drug Administration's control of experimentation on humans and changed the way new drugs are approved and regulated.Before the Thalidomide scandal in Europe, and Canada, U.S. drug companies only had to show their new products were safe.After the passage of the Amendment, an FDA New Drug Application (NDA) would have to show that a new drug was both safe and effective (previously the 1938 Food, Drug and Cosmetic Act was the main law that regulated drug safety).