Animal testing is used to develop medical treatments, determine the toxicity of medicine, check the safety of products destined for human use, and for other biomedical, commercial, and healthcare reasons. Research on living animals has been practiced since at least 500 BC.[2]

Early History

Descriptions of the dissection of live animals have been found in ancient Greek writings from as early as circa 500 BC. Physician-scientists such as Aristotle, Herophilus, and Erasistratus performed the experiments to discover the functions of living organisms. Vivisection (dissection of a living organism) was practiced on human criminals in Alexandria (ancient Egypt) and ancient Rome, but prohibitions in ancient Greece against the mutilation of the human body led to a reliance on animal subjects. Aristotle believed that animals lacked intelligence, and so the notions of justice and injustice did not apply to them. Theophrastus, a successor to Aristotle, disagreed, objecting to the vivisection of animals on the grounds that, like humans, they can feel pain, and causing pain to animals was an affront to the gods. [79][80]

Roman physician and philosopher Galen (130–200 AD), whose theories of medicine were influential throughout Europe for 15 centuries, engaged in the public dissection of animals (including an elephant), which was a popular form of entertainment at the time. Galen also engaged in animal vivisection in order to develop theories on human anatomy, physiology, pathology, and pharmacology. In one of his experiments, he demonstrated that arteries, which were believed by earlier physicians to contain air, actually contained blood. Galen believed that animal physiology was very similar to that of human beings, but despite this similarity he had little sympathy for the animals on which he experimented. Galen recommended that his students vivisect animals “without pity or compassion” and warned that the “unpleasing expression of the ape when it is being vivisected” was to be expected. [80][81][82]

French philosopher René Descartes (1596–1650), who occasionally experimented on live animals, including at least one rabbit, as well as eels and fish, believed that animals were “automata” who could not experience pain or suffer the way that humans do. Descartes recognized that animals could feel, but because they could not think, he argued, they were unable to consciously experience those feelings. [66][83]

English physician William Harvey (1578–1657) discovered that the heart, and not the lungs, circulated blood throughout the body as a result of his experiments on living animals. [84][85]

Animal Testing in the 1800s and Early 1900s

There was little public objection to animal experimentation until the 19th century, when the increased adoption of domestic pets fueled interest in an anti-vivisection movement, primarily in England. This trend culminated in the founding of the Society for the Protection of Animals Liable to Vivisection in 1875, followed by the formation of similar groups. [79][87]

One of the first proponents of animal testing to respond to the growing anti-testing movement was French physiologist Claude Bernard in his Introduction to the Study of Experimental Medicine (1865). Bernard argued that experimenting on animals was ethical because of the benefits to medicine and the extension of human life. [79]

Queen Victoria was an early opponent of animal testing in England, according to a letter written by her private secretary in 1875: “The Queen has been dreadfully shocked at the details of some of these [animal research] practices, and is most anxious to put a stop to them.” Soon the anti-vivisection campaign became strong enough to pressure lawmakers into establishing the world’s first law regulating the use of live animals in scientific research: Great Britain’s Cruelty to Animals Act of 1876. [15][88]

Russian physiologist Ivan Pavlov (1849–1936) demonstrated the “conditioned reflex” by training dogs to salivate upon hearing the sound of a bell or electric buzzer. In order to measure “the intensity of the salivary reflex,” wrote Pavlov, the dogs were subjected to a “minor operation, which consists in the transplantation of the opening of the salivary duct from its natural place on the mucous membrane of the mouth to the outside skin.” A “small glass funnel” was then attached to the salivary duct opening with a “special cement.” [75][86]

In The Principles of Humane Experimental Technique (1959), zoologist William Russell and microbiologist Rex Burch established the “Three Rs” of humane experimentation: Replacement (replacing the use of animals with alternative research methods), Reduction (minimizing the use of animals whenever possible), and Refinement (reducing suffering and improving animals’ living conditions). The “Three Rs” were incorporated into the United States’ federal Animal Welfare Act (AWA) of 1966 and formed the basis of many international animal welfare laws. [89][90][91]

Animals in Space and the Military

Since as early as 1948, animals have been used by the U.S. space program for testing such aspects of space travel as the effects of prolonged weightlessness. After several monkeys died in unmanned space flights carried out during the 1940s, the first monkey to survive a space flight was Yorick, recovered from an Aerobee missile flight on Sept. 20, 1951. However, Yorick died several hours after landing, possibly due to heat stress. The first living creature to orbit Earth was Laika, a stray dog sent into space on the Soviet spacecraft Sputnik 2 on Nov. 3, 1957. Laika died of “overheating and panic” early in the mission, according to the BBC. The record for the most animals sent into space was set Apr. 17, 1998, when more than 2,000 animals, including rats, mice, fish, crickets, and snails, were launched into space on the shuttle Columbia (along with the seven-member human crew) for neurological testing. [7][8][92][116]

Since the Vietnam War, animals have also been used by the U.S. military. The U.S. Department of Defense, for example, used 488,237 animals for research and combat trauma training (“live tissue training”) in fiscal year 2007, which included subjecting anesthetized goats and pigs to gunshot wounds, burns, and amputations for the training of military medics. In February 2013, after an escalation of opposition by animal rights groups such as People for the Ethical Treatments of Animals (PETA), Congress ordered the Pentagon to present a written plan to phase out live tissue training. The U.S. Coast Guard, however, which was at the center of a 2012 scandal involving videotaped footage of goats being mutilated as part of its live tissue training program, said in May 2013 that the program will continue. [6][93][94][95]

Regulations

A public outcry over animal testing and the treatment of animals in general broke out in the United States in the mid-1960s, leading to the passage of the AWA in 1966. An article in the Nov. 29, 1965, issue of Sports Illustrated about Pepper, a farmer’s pet Dalmatian that was kidnapped and sold into experimentation, is believed to have been the initial catalyst for the rise in anti-testing sentiment. Pepper died after researchers attempted to implant an experimental cardiac pacemaker in her body. [74][75]

Animal testing in the United States is regulated by the AWA, which was amended in 1970, 1976, and 1985. The AWA defines “animal” as “any live or dead dog, cat, monkey (nonhuman primate mammal), guinea pig, hamster, rabbit, or such other warm blooded animal.” The AWA excludes birds, rats and mice bred for research, cold-blooded animals, and farm animals used for food and other purposes. [3][27]

The AWA requires that each research facility develop an internal Institutional Animal Committee (more commonly known as an Institutional Animal Care and Use Committee, or IACUC) to “represent society’s concerns regarding the welfare of animal subjects.” The IACUC must comprise at least three members. One member must be a veterinarian and one must be unaffiliated with the institution. [3][27]

While the AWA regulates the housing and transportation of animals used for research, it does not regulate the experiments themselves. The U.S. Congress Conference Committee stated at the time of the bill’s passage that it wanted “to provide protection for the researcher . . . by exempting from regulations all animals during actual research and experimentation. . . . It is not the intention of the committee to interfere in any way with research or experimentation.” [66]

Animal studies funded by U.S. Public Health Service (PHS) agencies, including the National Institutes of Health (NIH), are further regulated by the Public Health Service Policy on Humane Care and Use of Laboratory Animals. [27]

All PHS-funded institutions must base their animal care standards on the AWA and the Guide for the Care and Use of Laboratory Animals (also known as “the Guide”), prepared by the Institute for Laboratory Animal Research at the National Research Council. Unlike the AWA, the Policy on Humane Care and Use of Laboratory Animals and the Guide cover all vertebrate animals used for research, including birds, rats and mice. The Guide “establishes the minimum ethical, practice, and care standards for researchers and their institutions,” including environment and housing standards and required veterinary care. The Guide stipulates that “the avoidance or minimization of discomfort, distress, and pain when consistent with sound scientific practices, is imperative.” [71]

The U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) reports the number of animals used for research each year, though it excludes animals not covered by the AWA. For fiscal year 2023 (the latest year for which data are available as of March 27, 2025), 774,065 animals were reported. Since the data excludes cold-blooded animals, farm animals used for food, and birds, rats, and mice bred for use in research, the total number of animals used for testing is unknown. Estimates of the number of animals not counted by APHIS range from 85% to 96% of the total of all animals used for testing. [1][2][26][65][72][152]

The USDA breaks down its data by three categories of pain type: animals that experience pain during their use in research but are given drugs to alleviate it; animals who experience pain and are not given drugs; and animals who do not experience pain and are not given drugs. [26]

The U.S. Food and Drug Administration (FDA), which regulates the development of new medications, states that “At the preclinical stage, the FDA will generally ask, at a minimum, that sponsors…determine the acute toxicity of the drug in at least two species of animals.” [73]

On Dec. 29, 2022, President Joe Biden signed the FDA Modernization Act 2.0. Sponsored by Senator Rand Paul (R-KY), the law updates the U.S. Federal Food, Drug, and Cosmetic Act by eliminating the requirement that pharmaceutical companies test new drugs on animals before human trials. The amendment does not prevent companies from performing animals tests, but makes the tests the choice of the company. [151]

The Modern Debate

In Animal Liberation: A New Ethics for Our Treatment of Animals (1975), Australian philosopher Peter Singer galvanized the animal rights and anti-testing movements by popularizing the notion of “speciesism”—the belief that some species should be treated as more important than other species—as something akin to racism, sexism, and other forms of prejudice. Addressing animal testing specifically, Singer predicted that “one day . . . our children’s children, reading about what was done in laboratories in the twentieth century, will feel the same sense of horror and incredulity . . . that we now feel when we read about the atrocities of the Roman gladiatorial arenas or the eighteenth-century slave trade.” [66]

In 1981, an early victory by then-fledgling animal rights group People for the Ethical Treatment of Animals (PETA) served to revitalize the anti-testing movement once again. A PETA activist working undercover at the Institute for Biological Research in Silver Spring, Maryland, took photographs of monkeys in the facility that had engaged in self-mutilation due to stress. The laboratory’s director, Edward Taub, was charged with more than a dozen animal cruelty offenses, and an especially notorious photo of a monkey in a harness with all four limbs restrained became a symbolic image for the animal rights movement. [96]

In 2001, controversy erupted over animal experiments undertaken by a veterinarian at Ohio State University. Dr. Michael Podell infected cats with the feline AIDS virus in order to study why methamphetamine users deteriorate more quickly from the symptoms of AIDS. After receiving several death threats, Dr. Podell abandoned his academic career. Over 60% of biomedical scientists polled by Nature magazine say “animal-rights activists present a real threat to essential biomedical research.” [35][97]

A 2007 report by the National Research Council of the National Academy of Sciences called for a reduction in the use of animal testing, recommending instead the increased use of in vitro methods using human cells. Though the report touted new technologies that could eventually eliminate the need for animal testing altogether, the authors acknowledged that “For the foreseeable future … targeted tests in animals would need to be used to complement the in vitro tests, because current methods cannot yet adequately mirror the metabolism of a whole animal.” [104]

In March 2013, the European Union banned the import and sale of cosmetic products that use ingredients tested on animals. Some proponents of animal testing objected, arguing that some animal tests had no non-animal equivalents. A spokesman for the trade association Cosmetics Europe stated it is likely “that consumers in Europe won’t have access to new products because we can’t ensure that some ingredients will be safe without access to suitable and adequate testing.” India and Israel have also banned animal testing for cosmetic products, while the United States has no such ban in place. [98][99]

China is the only major market where testing all cosmetics on animals is required by law, and foreign companies distributing their products to China must also have them tested on animals. China announced that its animal testing requirement will be waived for shampoo, perfume, and other so-called “non-special use cosmetics” manufactured by Chinese companies after June 2014. “Special use cosmetics,” including hair regrowth, hair removal, dye and permanent wave products, antiperspirant, and sunscreen, will continue to warrant mandatory animal testing. China’s National Medical Products Administration announced that animal testing for “ordinary” cosmetics (those that do not make claims such as “anti-aging”) will no longer be required as of May 2021. [43][65][114][149]

After ceasing to breed chimpanzees for research in May 2007, the U.S. National Institutes of Health announced in June 2013 that it would retire most of its chimpanzees (310 in total) over the next several years. While the decision was welcomed by animal rights groups, opponents said the decision would have a negative impact on the development of critical vaccines and treatments. The Texas Biomedical Research Institute released a statement claiming that the number of chimps to be retained (up to 50) was “not sufficient to enable the rapid development of better preventions and cures for hepatitis B and C, which kill a million people every year.” On Nov. 18, 2015 the U.S. National Institutes of Health announced that its remaining 50 research chimpanzees will be retired to the Federal Chimpanzee Sanctuary System. Gabon remains the only country in the world that still experiments on chimpanzees. [4][100][117]

The Environmental Protection Agency (EPA) released a plan on Sept. 10, 2019, to reduce studies using mammal testing by 30% by 2025 and to eliminate the mammal testing altogether by 2035. In Nov. 2019, the FDA enacted a policy allowing some lab animals used for animal testing to be sent to shelters and sanctuaries for adoption. The National Institutes of Health (NIH) adopted a similar policy in Aug. 2019 and the Department of Veterans Affairs (VA) did so in 2018. [131][146]

On Sept. 2, 2021, Mexico became the 41st country and first in North America to ban cosmetics testing on animals, according to the Humane Society International. [150]

Animal Testing and COVID-19

The COVID-19 (coronavirus) global pandemic brought attention to the debate about animal testing as researchers sought to develop a vaccine for the virus as quickly as possible. Vaccines are traditionally tested on animals to ensure their safety and effectiveness. News broke in Mar. 2020 that there was a shortage of the genetically modified mice that were needed to test coronavirus vaccines. [133]

Meanwhile, other companies tried new development techniques that allowed them to skip animal testing and start with human trials. Moderna Therapeutics used a synthetic copy of the virus genetic code instead of a weakened form of the virus. The FDA approved an application for Moderna to begin clinical trials on a coronavirus vaccine on Mar. 4, 2020, and the first participant was dosed on Mar. 16, 2020. [143][147]

A shortage of monkeys, including pink-faced rhesus macaques, threatened vaccine development at the beginning of the pandemic and as variants of COVID-19 were found. The monkeys were previously flown in from China, but a ban on wildlife imports from China forced researchers to look elsewhere, a difficult task as China previously supplied over 60% of research monkeys in the United States. [148]

Trump Administration Budget Cuts

An April 29, 2025, New York Times report found that 300 lab animals at the National Institute for Occupational Safety and Health lab in Morgantown, West Virginia, had to be euthanized due to budget cuts. The lab’s employees successfully relocated about 600 animals, mostly mice. Researchers at Harvard faced a budget freeze in April and were only able to save the rhesus macaques being used to develop a new tuberculosis vaccine with private funding. [153]

The reaction is split. On one hand, many are concerned about euthanizing animals for no reason other than a lack of funds and slowing down research. On the other hand, some approve of euthanizing the animals before they can be experimented on. [153]