Animal research is the use of non-human animals in scientific experiments to understand biology, develop medical treatments, and test the safety of drugs and consumer products. It spans a wide range of activities, from studying how genes work in mice to testing whether a new cancer drug is safe enough for human trials. Roughly 17 to 22 million animals are used annually in the United States alone, with about 85 percent being rats and mice.
Why Animals Are Used in Research
Animal research serves three broad purposes: basic science, medical development, and safety testing. Basic research uses animals to understand fundamental biology, things like how the immune system fights infection or how neurons communicate. This kind of work doesn’t always have an immediate medical application, but it builds the knowledge base that later breakthroughs depend on.
Translational and medical research is more goal-oriented. Scientists use animal models to study specific diseases, from cancer and heart disease to mental illness, drug addiction, and neurodegenerative conditions. Animals with biological systems similar to ours allow researchers to observe how a disease progresses and how potential treatments interact with a living body, something cell cultures and computer models still can’t fully replicate.
Safety testing is the third major category. Before a new drug, chemical, or consumer product reaches people, it typically goes through animal testing to flag toxic effects. For pharmaceutical development, this has historically been a regulatory requirement. The FDA has mandated that drug candidates undergo repeat-dose toxicity studies in animals, often lasting one to six months, before they can move into human clinical trials.
Which Animals Are Used
The vast majority of research animals are rodents. Rats and mice account for about 85 percent of all animals used in U.S. laboratories. Their short lifespans, well-mapped genetics, and small size make them practical for studies that need large sample sizes or multigenerational observation. Cats, dogs, and non-human primates together make up less than 2 percent of the total. Primates are typically reserved for research where no other species can provide relevant data, such as studies on complex brain function or certain infectious diseases.
Medical Advances Tied to Animal Studies
Many foundational medical breakthroughs trace back to animal experiments. In the late 1800s, Louis Pasteur used animal models to identify the bacteria behind anthrax and several other infections, then developed some of the earliest vaccines, including a rabies vaccine that worked in humans. His germ theory work also inspired Joseph Lister’s antiseptic surgical practices, which dramatically reduced deaths from post-surgical infection and childbirth complications.
Emil von Behring and Paul Ehrlich developed the first antitoxin for diphtheria using horse serum, work that earned von Behring the Nobel Prize in 1901. Von Behring also created an antitoxin for tetanus. Ehrlich later developed one of the first effective treatments for syphilis. These milestones laid the groundwork for modern immunology and drug development, and all relied on animal experimentation at critical stages.
The Three Rs: Ethical Principles
The ethical framework governing animal research centers on three principles known as the Three Rs, first described by researchers William Russell and Rex Burch. They are meant to be applied in order of priority.
- Replacement means using non-animal methods whenever possible. If a research question can be answered with cell cultures, computer simulations, or other alternatives, animals should not be used.
- Reduction means using the fewest animals necessary to get reliable results. Good experimental design and statistical planning help researchers avoid using more animals than the science requires.
- Refinement means minimizing pain and distress for animals that are used. This includes choosing less invasive procedures, providing appropriate pain relief, and improving housing and care conditions.
In practice, refinement shows up in detailed protocols. Federal guidelines require that surgical procedures only be conducted when animals are fully anesthetized. Paralytic drugs cannot be used as a substitute for anesthesia. Veterinary consultation is required for any potentially painful study, and pain must be treated whenever it’s identified. If a researcher believes pain relief would interfere with an experiment’s results, that exception must be scientifically justified and specifically approved by an oversight committee.
How Animal Research Is Regulated
In the United States, animal research is governed by the Animal Welfare Act and, for federally funded studies, by the Public Health Service Policy on Humane Care and Use of Laboratory Animals. Both require institutions to establish an Institutional Animal Care and Use Committee, or IACUC, that reviews and approves every research protocol involving animals before work begins.
An IACUC must have at least five members: a veterinarian, a scientist experienced with animal research, a non-scientist, and someone unaffiliated with the institution. This composition is designed to ensure that protocols are evaluated from both scientific and ethical perspectives. The committee inspects all animal facilities at least every six months and reviews ongoing research for compliance.
Researchers applying for federal funding must specify which species they plan to use, approximately how many animals, why animals are necessary, what steps they’ll take to minimize pain, and how animals will be humanely euthanized. No federally funded animal research can proceed without written institutional assurance and IACUC approval on file.
Public Opinion on Animal Research
Public support for animal research is mixed and depends heavily on context. A national survey published in the American Journal of Veterinary Research found that only 44 percent of respondents considered it acceptable to use animals in laboratory research. Cosmetic testing on animals received even less support, at 31 percent, roughly on par with approval for trophy hunting at 28 percent. People draw a clear line between research aimed at medical benefit and testing for consumer products like makeup or skincare.
Alternatives Gaining Ground
Technology is starting to offer viable substitutes for some animal studies. Organ-on-a-chip devices are microfluidic platforms that mimic the function of human organs on a small scale, allowing researchers to test drug effects on living human tissue outside the body. Organoids, which are self-organizing 3D tissue structures grown from human cells, offer another approach. Computer modeling can simulate how drugs move through and interact with the body.
These tools have real limitations, though. Organ-on-a-chip devices still lack functional blood vessel networks, nerve connections, and immune components, all of which are critical for mimicking how organs actually behave in a living body. The materials commonly used to build these chips can absorb drug molecules, throwing off the accuracy of toxicity measurements. Organoids vary in size and shape, making them difficult to standardize across labs.
Regulatory momentum is shifting regardless. In late 2022, Congress passed the FDA Modernization Act 2.0, which removed the requirement to use animal studies for certain drug applications and explicitly authorized non-animal alternatives like cell-based assays and computer models. The FDA can now allow sponsors to skip animal testing if they provide sufficient data from alternative methods, evaluated on a case-by-case basis. For some products, a single animal species study paired with non-animal data may be enough, and in certain cases, an entirely animal-free approach may be accepted.
This represents a significant policy shift, but it doesn’t mean animal research is disappearing. For complex questions involving whole-body systems, immune responses, or long-term disease progression, animal models remain the most complete tool available. The practical reality is a gradual transition: animals used where alternatives can’t yet deliver equivalent data, and newer technologies steadily expanding the range of questions they can answer.