The 3Rs (replacement, reduction, refinement) are a set of principles that provide an internationally accepted framework toward achieving more humane scientific research by minimizing animal distress. William Russell and Rex Burch—who coined the 3Rs in their 1959 landmark book, The Principles of Humane Experimental Technique—considered the “absolute replacement” of animals to be the “absolute ideal.” Despite this, refinement (improving conditions for animals currently living in laboratories) has been implemented more widely than replacement, generally because the absolute replacement of animals with nonanimal methods is more challenging.
A common misconception is that recent technological and scientific advancements in so-called new approach methodologies (NAMs) allow for full replacement of all ongoing animal experimentation. The reality is more nuanced. Absolute replacement is more difficult for research that is “basic” in nature—exploratory studies meant to advance general scientific knowledge, such as understanding the progression of disease. We are much closer to being able to fully replace animals for regulatory testing purposes, such as testing the safety of drugs and products before they are used in humans or testing the toxicity of chemicals that may be found in the environment. Unfortunately, many more animals are used for basic research purposes than for testing purposes.