Animal experimentation, also called animal testing, has contributed to many important scientific and medical discoveries. Breakthroughs include the development of many antibiotics, insulin therapy, modern anesthesia, vaccines for whooping cough and other diseases, the use of lithium in mental health treatments, and the discovery of hormones. Studies using animals have also led to the development of new surgical techniques and medical devices. Scientists use animals for testing the safety of products, known as toxicology testing, and for evaluating the effects of biological, nuclear, and chemical weapons. Unlike field research, which involves observing animals in their natural habitats, animal experimentation takes place at laboratories in universities, medical schools, government facilities, and commercial facilities, such as those run by pharmaceutical and cosmetics manufacturers. Experiments on animals can involve testing drugs and other substances as well as performing behavioral tests, such as those conducted on dogs by Russian physiologist Ivan Pavlov in the early twentieth century.

While acknowledging the advances brought by animal experimentation, many people object to the use of animals in scientific studies because the animals are denied their freedom and often suffer serious injury and discomfort. Other people identify certain practices used in animal studies as cruel while still recognizing the benefits of using live animals when no alternative is available. Proponents of animal experimentation maintain that these studies provide benefits to humans that cannot be achieved through other means. Conversely, critics of using animals to learn more about humans contend that the differences between humans and nonhuman species are too great for such studies to produce meaningful results. In response, proponents note that humans are not the only beneficiaries of this type of research. Many experiments are carried out to further veterinary treatments and services, improve environmental protection efforts, and better understand diseases that affect nonhuman animals and plants.

Congress has enacted several pieces of legislation to regulate animal experimentation and prevent animal abuse, including the Animal Welfare Act (AWA), first passed as the Laboratory Animal Welfare Act in 1966, and the Improved Standards for Laboratory Animals Act (ISLAA), passed as part of the Food Security Act of 1985. In 2017 Representative Martha McSally (R-AZ) introduced the Humane Cosmetics Act, which aims to phase out the use of animal testing in the cosmetics industry in the US House of Representatives. In 2018 Representative Mike Bishop (R-MI) and Senator Jeff Merkley (D-OR) introduced the Kittens in Traumatic Testing Ends Now (KITTEN) Act, which would ban the use of cats in any painful or stressful experiment, to their respective chambers of Congress. As of March 2019, however, no action has been taken on either the Humane Cosmetics Act or the KITTEN Act. Several private companies have voluntarily agreed not to test their products on animals. Some cosmetic manufacturers, including Procter and Gamble and Unilever, have called on the industry to adopt a global ban on testing. In 2019 the efforts of animal rights activists led high-profile companies in other fields, such as food-manufacturers Kellogg Company and Hershey Company, to affirm their opposition to animal testing and end their involvement in such experimentation.

Regulations on Animal Test Subjects

As reported by the US Department of Agriculture (USDA), 792,168 animals were used in experiments at USDA-registered facilities in fiscal year 2017. The total includes only animals protected by the AWA and omits amphibians, birds, fish, mice, rats, and reptiles, all of which account for the majority of animals used in scientific studies. Of the animals monitored by the USDA, the most commonly used is the guinea pig, which has been widely used for experimentation since the late 1800s, leading it to become synonymous with a subject of any experiment. Guinea pigs, rabbits, and hamsters account for more than half of the animals in the totals reported by the USDA. The other reported test subjects include nonhuman primates, dogs, pigs, cats, and sheep.

Laboratories obtain animals for their experiments through three types of dealers: those licensed by the USDA as Class A dealers, those licensed as Class B dealers, or those not licensed at all. Class A dealers breed and raise their animals in a closed, regulated environment. Class B dealers are less regulated and purchase or obtain animals to resell. The USDA excuses some breeders and dealers from licensing because of the type, amount, or intended use of the animals. Some states require research facilities to purchase solely from Class A dealers. Class B dealers often acquire animals from animal shelters and then sell them to research facilities.

Investigations in the 1990s revealed that some Class B dealers abducted family pets from the street. This phenomenon led lawmakers to introduce the Pet Safety and Protection Act as an amendment to the AWA in 1996. The provision would have banned research facilities from using any dog or cat that was not obtained from a legal source. The amendment was not adopted, nor was it adopted when reintroduced in nearly every subsequent session of Congress, most recently in 2019. Despite the amendment repeatedly failing to become law, the National Institutes of Health (NIH) adopted rules in 2012 and 2014 that ended NIH funding for research involving cats and dogs from Class B or unlicensed dealers. Likewise, a provision to the Consolidated Appropriations Act of 2016 prevents the USDA from using any funds appropriated by the act to provide or renew licenses for Class B dealers. The law has effectively made it impossible for Class B dealers to obtain licenses to sell animals for research purposes. Some critics have questioned the need for the Pet Safety and Protection Act, noting that cats and dogs make up only a small portion of the animals used in experiments.

Scientists in certain fields have favored using nonhuman primates in experiments because they closely resemble humans in physiology. The National Aeronautics and Space Administration (NASA), for example, sent several nonhuman primates into space before sending human astronaut Alan Shepard in 1961. Many laboratories worked with chimpanzees throughout the twentieth century. Animal behaviorists, noting the chimpanzee's intelligence and capacity for emotion, raised concerns that the use of chimpanzees in experiments amounted to torture. The Institute of Medicine deemed the use of chimpanzees in scientific research unnecessary in a 2011 report commissioned by the NIH. This report was followed by a proposal by the United States Fish and Wildlife Service (USFWS) to include captive chimpanzees, such as those used in research facilities, on the list of animals protected by the Endangered Species Act; chimpanzees in the wild had already been protected by the act since 1990. In 2013 the NIH announced its intentions to stop providing funding or granting research requests for experiments involving chimpanzees, and the USFWS proposal was finalized in 2015. Many NIH chimpanzees have since been moved to federal sanctuaries. However, scientists have chosen not to resettle many older research chimpanzees in sanctuaries because of concerns the move would worsen their health.

Alternatives to Animal Testing

Animal rights advocates and members of the scientific community have pushed for the use of alternatives to animal experimentation. The pursuit of alternatives has largely centered on concepts first introduced in 1959 by British zoologists W. M. S. Russell and R. L. Burch in The Principles of Humane Experimental Technique. Russell and Burch framed their proposal around three Rs. They suggested that experimentation should replace animal subjects with something else, such as non-sentient material or less sentient animals; reduce the number of animal subjects used experimentally while increasing the amount of data obtained; and refine living conditions and experimental procedures for animal subjects to reduce pain and discomfort.

The NIH established the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) in 2000 as part of the National Toxicology Program Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) to promote and regulate alternatives to animal testing. In addition to government programs, animal rights advocacy groups, such as People for the Ethical Treatment of Animals (PETA) and the American Fund for Alternatives to Animal Research (AFAAR), also contribute funding to develop alternative research methods. AAALAC International, formerly known as the Association for Assessment and Accreditation of Laboratory Animal Care, distributes up to four $5,000 prizes each year to researchers that make significant contributions to improving the nature of animal research. The awards are a component of the organization's Global 3Rs Awards program, named for the principles put forth by Russell and Burch.

Companies and research facilities, however, can be slow to adopt alternatives. In 2009, for example, the Organization for Economic Cooperation and Development (OECD) approved two alternatives to the Draize test, a research method that involves applying chemicals directly to the eyes or skin of animals, typically rabbits. The test is widely condemned by animal rights activists. As of 2019, despite the availability of these alternatives, scientists continue to perform the Draize test, arguing that no single test has proven able to replicate the full benefits of the Draize test.

Technological advances have enabled scientists to perform many experiments without using live animals. Invasive animal experimentation that involves performing surgery on a living animal can be referred to as vivisection, as opposed to dissection, which is surgery performed on a deceased animal. The term vivisection, however, is typically used by opponents of animal experimentation and avoided by scientists. Researchers have developed ways to obtain data without using live specimens by experimenting on cells and tissues, rather than the entire living organism; these procedures are referred to as in vitro experiments. In many in vitro experiments, human cells and tissues can be used. Proponents argue that this method produces data that is more relevant to human safety. Critics of in vitro methods argue that operating on a live animal provides more accurate data because the effects on the entire organism can be observed.

US schools began incorporating dissection into biology instruction in the 1920s, with the practice becoming widespread by the 1960s. A 2014 survey conducted by the National Association of Biology Teachers found that 84 percent of biology teachers and 76 percent of biology students were using dissection in the classroom. Many of the responding teachers, however, reported that their schools were shifting away from dissection and pursuing alternatives, such as virtual dissection programs, 3-D models, and videos, largely in response to student requests. Educators also reported using these alternatives alongside traditional hands-on dissection.

In the early 2000s researchers began developing microdevices referred to as organs-on-a-chip (OOCs), which use cell cultures to imitate a human organ and determine how that organ would respond to different chemicals and other stimuli. OOCs are approximately the size of a deck of playing cards and have been developed to imitate lungs, hearts, kidneys, skin, eyes, and entire organ systems. In 2018 researchers successfully tested OOCs that imitated interconnected organ systems and could produce data for twenty-eight days, indicating that a microdevice could likely support an entire ""human on a chip."" In some cases, computer models can simulate the effects of diseases and medicines on the human body with greater accuracy than animal subjects. Research methods that substitute computer models for live animals are referred to as in silico experiments.

Despite efforts to reduce the number of animals used in scientific studies and minimize the pain and distress that animal subjects experience, some animal rights activists believe that the benefits of animal experimentation do not justify the cruelties involved. These activists call for an end to all animal testing. Extremist groups have engaged in criminal activity to prevent animals from being used in experiments. In the late 1970s, radical animal rights groups began targeting companies and research facilities, using terrorist strategies to disrupt these industries and promote their extremist platform. Actions by members of radical groups such as the Animal Liberation Front (ALF) and Stop Huntingdon Animal Cruelty (SHAC) caused millions of dollars of damage to industries.

To protect research companies and other commercial enterprises vulnerable to animal rights violence, Congress passed the Animal Enterprise Protection Act of 1992 and the Animal Enterprise Terrorism Act of 2006. Critics of these laws note that both bills received support from biomedical and agri-business lobbying groups. Additionally, critics note that both laws include language that criminalizes activities protected by the First Amendment, such as picketing and leading boycotts, if they interfere with a company's ability to make money. In 2015, two animal rights activists, Kevin Johnson and Tyler Lang, challenged the constitutionality of the Animal Enterprise Terrorism Act after they were charged with violating the act for vandalizing a mink farm and setting hundreds of animals free. However, the United States Court of Appeals for the Seventh Circuit ruled that the law was constitutional in November 2017.