In this blog post, I will examine the necessity and limitations of animal testing based on the two values of animal rights and human welfare, and explore alternative methods to reduce animal testing as well as the significance of the 3Rs principle.
Can animal testing and animal rights coexist?
For a long time, humans have conducted numerous animal experiments to develop new drugs. In 1903, an incident occurred at University College London (UCL) in which William Baileys performed a live dissection on a brown terrier during a lecture; this event later became known as the “Brown Dog Affair.” This incident sparked a major debate over the ethics and necessity of animal testing, and the pros and cons of such testing have remained a constant subject of social debate ever since. Some view animals as friends, while others see them as tools for research aimed at advancing medical technology. However, humans have a responsibility to respect and protect animal rights, and animal experimentation does not guarantee high efficiency in all cases. Therefore, I argue that rather than unconditionally expanding the use of animal experimentation, we should strictly limit it to necessary cases and reduce its use by replacing it with alternative methods whenever possible.
First, animal experimentation must be reduced because it can severely infringe upon the inherent rights of animals. Since animals are beings that feel pain, behave, and live just like humans, I believe they have the right not to suffer unnecessarily and to have their lives respected. However, laboratory animals are used in research without having the right to choose whether or not to be subjects of experimentation, and in the process, they suffer physical harm and may even die. Consequently, they are sacrificed against their will to promote human welfare or develop new technologies. Laboratory animals cannot express their grievances or objections in human language. However, this does not mean they do not feel pain. Laboratory animals, too, do not want to be treated cruelly and wish to avoid unnecessary suffering. Therefore, when humans unilaterally determine the fate of laboratory animals, there is a risk that they will fail to give sufficient consideration to the value of animal life and infringe upon their rights. Consequently, to protect animal rights, we must reduce unnecessary animal experimentation and, whenever possible, replace it with methods that do not involve animals.
Which should take precedence: human welfare or animal rights?
However, there are also those who actually accept animal experimentation. They view animals as beings of a lower order than humans—organisms that do not need to enjoy the same rights as humans—and argue that even if animals do have rights, they cannot fully exercise them in the same way humans do. Furthermore, some people prioritize human welfare over animal rights. They believe that humans possess greater value than animals because they think differently, know how to use tools, create works of art, and possess various other abilities. Consequently, they argue that animal testing is essential because it is more important to develop the medicines necessary to prolong valuable human lives and enable humans to live better lives.
However, the belief that it is acceptable to cause suffering to animals while prioritizing only human well-being may reflect an attitude that fails to fully consider humanity’s ethical responsibilities. Since animals are sentient beings capable of feeling pain, humans must strive to understand and alleviate their suffering. Therefore, shouldn’t humans protect animal rights more vigorously? Shouldn’t we reduce the suffering animals endure due to unnecessary experiments? Typical examples of experiments that can cause significant suffering to animals include the LD50 test and the Draize eye irritation test. The LD50 test involves administering a toxic substance to estimate the dose that causes 50% of the test animals to die within a specified period. In the traditional method, animals were administered the substance at various doses, and toxicity and mortality rates were observed.
However, to reduce animal sacrifice even in the evaluation of acute toxicity, methods such as the fixed-dose method, acute toxicity grading, and the dose-response method are now being utilized, moving away from the traditional LD50 test as it was originally conducted. The Draize eye irritation test primarily involves instilling a test substance into a rabbit’s eye and observing the damage that occurs to the cornea, conjunctiva, and other tissues. Ethical concerns have been raised regarding this process, as it can cause pain and eye damage to the animals. There is also the limitation that it is difficult to assume that the results of animal testing can be directly applied to humans. In particular, various animal-free methods are currently being developed, such as three-dimensional reconstructed human cornea and skin models similar to human tissue, cell-based assays, and computer models, and in some fields, these are being utilized to replace or supplement existing animal testing. The U.S. Food and Drug Administration (FDA) is also promoting guidelines and policies, effective in 2026, to reduce or replace animal testing in new drug development by utilizing New Approaches to Medicine (NAMs). If these methods are further developed and validated, the likelihood of obtaining the necessary information for humans without harming animals will increase.
Is animal testing sufficiently efficient from a medical standpoint?
As briefly mentioned earlier, the use of animal testing should be phased out because it does not guarantee high efficiency in all medical research. Therefore, from a medical perspective, humans need to reconsider the efficiency of animal testing. Since animals and humans do not have completely identical bodily functions and physiological characteristics, differences may arise in the results even when animal testing is conducted, and there is no guarantee that the reactions observed in animals will manifest identically in humans. Ray Greig and Jean Swingle Greig pointed out the limitations of drug research using animal models, arguing that it is difficult to guarantee that drug responses observed in animals will manifest identically in humans. In fact, responses to drugs can vary by species, and the difference between animal and human physiological characteristics is a critical issue that must be considered when applying animal testing results to humans. In particular, as demonstrated by the thalidomide case, drug responses can vary significantly depending on the species. At the time, the teratogenic potential of thalidomide was not properly identified in some animal studies, but its teratogenic effects were later confirmed in various animal species, including rabbits. Rather than simply demonstrating that animal testing is meaningless, this case illustrates that there are clear limitations to directly applying results obtained from specific animals to humans, and that species-specific differences must be taken into account. Therefore, even in the medical field, the results of animal testing should not be trusted unconditionally; instead, their applicability to humans must be carefully evaluated.
However, some people believe that, despite these limitations, the results obtained through animal testing contribute to medical progress and remain reliable information. They argue that animal testing not only verifies the efficacy and safety of new products or treatments but is also used to predict the effects of products such as pharmaceuticals, pesticides, cosmetics, and food on the human body. In particular, one can cite the development and research of drugs such as tamoxifen as evidence that preclinical studies—including animal testing—have served as a crucial step in medical progress. Tamoxifen was developed in the 1960s and subsequently became an important anticancer drug after being used to treat breast cancer. Based on such examples, people believe and argue that preclinical research—including animal testing—has contributed significantly to the advancement of modern medicine.
However, the validity of animal testing as a whole cannot be judged based on a single success story involving a specific drug. This is because, due to differences between humans and animals, animal testing does not always guarantee how accurately certain results can be applied to humans. In fact, there are cases that demonstrate the potential for animal testing to provide misleading information to humans.
For example, in past animal experiments related to smoking, no evidence of lung cancer similar to that observed in humans was found in the animals’ lungs; if the relationship between smoking and lung cancer were judged based solely on these results, it could lead to erroneous conclusions regarding human health. Another example is thalidomide. Thalidomide, which went on sale in Europe in 1957, was used to alleviate morning sickness in pregnant women, but it was later discovered that women who took it during pregnancy gave birth to children with severe congenital malformations. The fact that preclinical trials at the time were insufficient and that responses varied depending on the animal species demonstrates that it is difficult to fully predict the risks to humans based solely on animal testing results. Subsequent studies also confirmed that thalidomide can cause birth defects in rabbits and certain other animal species. Therefore, rather than interpreting the thalidomide case simply as an argument that “animal testing was inaccurate,” we must accept it as a lesson that, when applying the results of animal testing to humans, we must consider species differences, experimental design, and the scope and limitations of the research. Ultimately, while animal testing can provide useful information for humans, it cannot accurately predict all outcomes in humans on its own; therefore, we must review both the necessity and limitations of animal testing while working to reduce unnecessary experiments.
What measures are needed to reduce animal testing?
In conclusion, just as human life is precious, animal life must also be respected; therefore, we must protect animal lives and prevent unnecessary sacrifices. Considering the need to uphold animal rights and the limitations of animal testing, we should reduce animal testing within necessary limits rather than unconditionally expanding it. The 3Rs are a key principle in this regard. The 3Rs stand for Replacement, Reduction, and Refinement. Replacement involves substituting animal testing with non-animal methods—such as cells, tissues, or computer models—whenever possible; Reduction means using only the minimum number of animals necessary to achieve the research objectives; and Refinement involves improving the animals’ housing conditions and experimental procedures to minimize pain and suffering. The 3R principles were first proposed by William Russell and Rex Burch in 1959 and remain an important framework that balances the ethical and scientific validity of animal testing. Furthermore, with recent advancements in New Alternative Methods (NAMs)—including tests using human tissues and cells, microphysiological systems such as organ-on-a-chip, computer simulations, and artificial intelligence—the potential to replace or reduce animal testing has grown significantly. However, since current alternative methods cannot fully replicate all biological phenomena and diseases, efforts to replace and reduce animal testing must be made within scientifically validated limits. Moving forward, we must find ways to continue the research necessary for medical advancement while protecting animal lives by more actively utilizing the 3R principles and new alternative testing methods. Ultimately, reducing animal testing does not mean abandoning human lives; rather, it means rethinking the direction of science and medicine while showing greater respect for the lives of both humans and animals.
