Alternatives to Animal Testing

science tubes in lab

Advances in science are transforming how scientists study health and disease. Biomedical and behavioral research can involve working with animal models, cells in test tubes, computer modeling, and clinical studies with people. Each research approach is critical to advancing our knowledge of health and disease.

Over the last decade, improved technological capabilities enable scientists to reduce their reliance on animal models for specific types of studies. These advances are important because testing in animals can pose ethical issues, takes significant time and resources, and the relevance to human health is not always certain.

Recent advances in alternative methods, such as computational, biochemical, or cell-based model systems that can replicate human biology, have been shown in some cases to perform the same as or even better than standard animal models. These “New Approach Methodologies” (NAMs, sometimes called Novel Alternative Methods, Non-Animal Methods, or New Alternative Methods) can provide a complementary approach to traditional models. They can offer a way to improve understanding of the human system and its susceptibility to toxic effects, and to discover effective treatments for human conditions.

NIEHS has been a leader in the development of NAMs to reduce the use of animals and increase the human relevance of models in health effects testing. NIEHS is working with the scientific community and other stakeholders to increasingly apply these methods to policy and regulatory decision-making processes or to replace traditional testing requirements.

The 3Rs

NIEHS is also committed to efforts that replace, reduce, or refine (the “3Rs”) the use of animal models in studies. This concept of replacing, reducing, or refining animal use in research and testing was first described more than 65 years ago. The 3Rs became a tenet for the scientific community to address animal welfare in a meaningful way.

  • Replacing: The method substitutes traditional animal models with non-animal systems such as computer models or biochemical or cell-based systems, or one animal species is replaced with a less developed one (for example, replacing a mouse with a worm).
  • Reducing: The method decreases the number of animals required for testing to a minimum while still achieving testing objectives.
  • Refining: The method eliminates pain or distress in animals, or enhances animal well-being, such as by providing better housing or enrichment.

Types of Alternative Methods

The scientific toolbox used for toxicological assessment continually expands. In a 2023 report, NIH categorized NAMs approaches into three general categories. Definitions and examples of each method are below.

In chemico: Experiments performed on biological molecules, such as proteins and DNA, outside of cells, which may be used to study how these molecules interact with each other and with drugs.

In silico: Experiments performed by computing platforms or custom hardware, encompassing mathematical modeling and simulation, machine learning, and other computational techniques.

  • Computational model is a general term describing the use of computers to simulate complex systems, such as those that can be used as a NAM.
  • Artificial intelligence and machine learning (AI/ML) approaches can enhance and support human intellect in assessing the safety of chemical exposures. For example, advanced computer simulations can be used to model biological processes and predict the effects of previously untested chemicals and drugs.

In vitro: Experiments performed on cells outside of the body, including various types of cell, organoid, and tissue culture techniques.

  • These methods may involve culturing cells in the laboratory and can take advantage of high-throughput screening of large numbers of chemical compounds.
  • Microphysiological systems or organs-on-chips are complex, cell-based devices that mimic key physiological aspects of tissues or organs by incorporating microenvironments that align with those in the human body. A particular system might incorporate flow and shear stress, appropriate pH and oxygen levels, biochemical and electrical stimuli, and other factors that replicate various features of animal-based models.
  • Mini-organs or organoids are 3D tissue-like structures, derived from stem cells, that closely replicate the complexity and function of human organs. These tiny, artificially grown tissues contain various specialized cell types similar to those found in full-sized organs.

Different human populations experience different levels of susceptibility to toxic effects from chemical exposure, presenting a complex problem for chemical risk assessment. Alternative methods, such as those above, could provide more rapid and human-relevant techniques to assess chemical safety for diverse communities affected by environmental exposures. Alternatives to animal testing can be used for toxicological research, such as chemical safety and drug effectiveness testing, or other types of biomedical research that examine biological mechanisms of disease.

NIH leadership for NAMs

The NIH Common Fund’s Complement Animal Research In Experimentation program (Complement-ARIE) aims to speed the development, standardization, validation, and use of human-based NAMs. It will significantly advance the understanding of human health and disease and approaches to basic, translational, toxicological, and clinical research. NIEHS plays a lead role in planning activities for this program.

Complement-ARIE brings together many areas of expertise through a consortium of researchers in the following efforts:

  • Technology centers will develop NAMs projects to fill in areas of greatest need. Projects will emphasize biological complexity, high throughput techniques, combining approaches, and data sharing.
  • A resource coordinating center will create integrated data structures and a searchable NAMs repository.
  • A validation and qualification network will accelerate deployment and regulatory approval of NAMs for biomedical research.
  • Community engagement and training will promote the development of an inclusive and diverse biomedical research workforce with the skills to build and use new NAMs.
  • Strategic engagement with key partners will advance opportunities in the development and use of NAMs in basic, translational, and clinical research.

What is NIEHS Doing?

NIEHS is committed to advancing new approaches to safety testing of chemicals and medical products in the United States and to the ethical and responsible conduct of necessary animal research.

  • NIEHS leads the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM), which coordinates the activities of 17 federal regulatory and research agencies to work together to develop and evaluate new, improved, and alternative test methods and strategies to replace, reduce, or refine animal use.
  • The NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) is an office within the Division of Translational Toxicology at NIEHS that supports ICCVAM activities, as well as activities with external stakeholders and international organizations. NICEATM is charged with evaluating and promoting methods that replace, reduce, or refine the use of animals for chemical safety testing.
    • NICEATM supports a range of computational toxicology projects that use mathematics, informatics, and computer models to better understand how to predict the toxic effects of chemicals.
    • NICEATM helped develop an online data resource called the Integrated Chemical Environment (ICE) that supports the development, evaluation, and application of NAMs.
    • In support of Complement-ARIE, NICEATM is conducting a landscape analysis of existing NAMs efforts in health and disease and supporting the validation and qualification network.
  • The Scientific Advisory Committee on Alternative Toxicological Methods (SACATM) includes experts from academia, industry, and animal welfare organizations. The committee meets annually to advise the NIEHS director on the development, evaluation, and implementation of new approach methodologies undertaken by NICEATM and ICCVAM.

Additionally, the NIEHS Division of Translational Toxicology is part of the Toxicology in the 21st Century (Tox21) program, a federal research collaboration developing high-throughput tests and NAMs that can rapidly determine whether chemical  adversely affect human health.

For example, under Tox21, researchers at NICEATM developed the Tox21BodyMap to predict which organs in the human body may be affected by a chemical. The tool is based on data from 971 high-throughput screening assays that evaluated approximately 10,000 unique chemicals. The Tox21BodyMap will help scientists generate hypotheses to test and prioritize chemicals for toxicity testing.

Extramural research

NIEHS also funds a variety of projects to develop alternative testing methods through grants to external researchers and small businesses.

For example, NIEHS grantees from the Massachusetts Institute of Technology developed a new toxicity test that can accurately measure the impact of chemicals on cell survival in a matter of days. The findings could allow academic researchers and drug companies to rapidly evaluate environmental contaminants and new drugs for possible harmful effects.

Scientists supported by the NIEHS Superfund Research Program developed an innovative template-and-anchor model to determine the health effects of exposure to dioxins. Researchers used the model to combine publicly available data on exposures and on known health outcomes to assess the overall risk dioxins could pose to health. It is an example of how a computational approach can provide a promising novel approach methodology to predict health risks associated with chemical exposures.

Researchers partially funded by NIEHS developed an in-silico method–a computer simulation tool–for genetic research that may partially replace the need for genetically modified animals. Called the Gene Knockout Inference (GenKI), the tool allows scientists to simulate the relationship between genes in individual cells so they can study which genes affect cellular functions. Future refinements to the tool may enable its predictive power.

Further Reading

Stories from the Environmental Factor (NIEHS Newsletter)

Additional Resources

  • Animals in NIH Research - Research with laboratory animals (also called “animal models”) has provided the foundation for safe and effective life-saving treatments for many diseases and conditions affecting humans. All federally funded research animals are protected by laws, regulations, and policies to ensure the smallest possible number are used to produce reliable results. NIH is committed to their proper care.
  • Catalyzing the Development and Use of Novel Alternative Methods – The report of an NIH working group on NAMs (December 2023). NIH Director Monica Bertagnolli, M.D., accepted this working group’s recommendations and issued an NIH Statement on catalyzing the development of novel alternative methods (February 2024).
  • ChemMaps is a publicly accessible web tool for exploring environmental chemicals and predicting their risk. The tool includes DrugMap, which lists more than 8,000 drugs, and EnvMap, which lists more than 47,000 chemicals of relevance to NIEHS and EPA.
  • The Organisation for Economic Co-operation and Development (OCED) assists its 38 member countries, including the U.S., in developing and implementing policies and instruments that make systems for managing chemicals as efficient and robust as possible, while protecting human health and the environment. The Test Guidelines Programme advances alternatives to animal testing internationally. Data generated in one country using these methods are accepted in all member countries, reducing the need for redundant testing for regulatory authorities.

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