Essential animal experiments and transferability of the results to humans

Breakthrough innovative medicines and treatments are partly the result of animal experiments. Given the biological similarities between humans and animals, it is possible to transfer the results of experiments.

1. Introduction

In pharmaceutical research, animal experiments take place in the preclinical phase of the long path that leads to a market- ready medicine. It usually takes many years to reach this stage. Researchers generally test hundreds of thousands of substances before they find one with the potential to inhibit or positively influence the course of a particular disease. At first, the experiments in this journey of discovering new active pharmaceutical ingredients (APIs) involve solutions and cell cultures. Animal experiments only take place once certain conditions have been fulfilled. They are used to determine how the drug candidate is metabolised by the organism and if it produces detrimental effects. Only when a substance has successfully completed all the prescribed preclinical trials – in other words, once it has been shown to be safe and effective in cell cultures and animal experiments – can it be tested in clinical trials in humans. Why only then?

2. Ethics and safety

The international community has committed to ethical and legal principles for human research by adopting various reports and declarations. For example, the World Medical Association’s Declaration of Helsinki of 1964 states that the testing of new treatments must protect the health and interests of the people taking part in research. The Declaration of Helsinki became and remains the basis of many countries’ legislation on biomedical research. Accordingly, clinical trials involving a small number of healthy volunteers and subsequent trials in patients are only permissible today if the associated risks have been minimized or can be excluded.

Ethical principles applicable for human research


The Declaration of Helsinki (1964) describes the balance that has to be struck between the need to obtain reliable medical knowledge and the need to protect the health and interests of the people taking part in research.


The Belmont Report (1978) sets out moral principles, such as respecting human dignity.

This means that as much as possible has to be known about the safety and efficacy of a new API before it enters clinical trials in humans. To ensure this is the case, animal experiments are still prescribed in addition to methods that do not involve animals, such as cell and tissue cultures, computer simulations or what is known as organ-on-a-chip, which reduce or partially replace animal experiments. One of the aims of animal experiments is often to identify the harmful effects of a new API at an early stage. Ensuring the animals’ well-being to the maximum extent possible is a priority in such cases. Alternative methods that do not involve animals, such as those mentioned above, are now commonplace in biomedical research. They are frequently used for biological systems that have already been extensively researched.

Same structures and physiological processes
The process of programmed cell death plays an important role in the development of various diseases, including cancer. In 2002, the process was even found to exist in nematodes, tiny organisms just a few millimeters in length.

3. When there aren’t enough volunteers

In addition to basic ethical considerations, one of the reasons researchers use animals for experiments is because humans are not always ideal subjects for investigating biomedical issues. Organisms that reproduce quickly, such as zebrafish or mice, are more suitable, particularly for researching hereditary diseases.
There are often insufficient human volunteers for scientists to be able to research the genetic, physiological or anatomical causes of many rare diseases. This means that animal experiments are needed to gain an understanding of the disease or to develop APIs to treat it. But why are experiments involving animals even suitable in the first place?

4. Evolutionary kinship

Every medicine, every treatment and almost all medical devices that are used worldwide to alleviate disease or help patients recuperate were developed with the aid of animal experiments. There are various reasons why animal experiments are necessary to research diseases and develop new medicines and innovative treatments. One key reason is that such research is by its very nature biology-driven. Basic biological research is impossible to conduct without living organisms. Without biological research involving living organisms, we would not now know how animals survive in their environment, for example, and what they need to do so. This knowledge also benefits medicine and pharmaceutics because things that make animals ill are frequently also harmful to humans.

5. Valuable pointers on the cause of disease

In evolutionary terms, animals and humans are related. They share common ancestors and thus also biological similarities, even if these are not always equally pronounced. As evolution has progressed, nature has retained a large number of processes. Hence research with animals can deliver valuable pointers on the cause of diseases and the effect of medicines. It provides information on desirable effects and brings around 70 percent of undesirable effects to light.

6. Results are transferable

Choosing a suitable animal model is key to ensuring that the results of animal experiments can be transferred to humans. That means that the animal must be as similar as possible to humans both genetically and in terms of the biological functions to be investigated. This is the case with zebrafish, fruit flies and rodents, particularly mice. Mice and humans share a very similar development, physiology and genome. The genetic and physiological match between the two species is around 95 percent. This is why mice are the species most commonly used in preclinical research involving animals. Mouse models provide information about human health and disease. A large number of mouse models are now in use in research in Europe and around the world. In addition, disease models have been developed, phenotyped and archived for research. In the disease model, a disease is artificially induced in the test animal. The researchers make sure that the disease process in the mouse is generally the same as if the disease had broken out by itself. As a result it is possible to make inferences about the situation in humans. Differences obviously remain, however. This is why any medicine, new therapy or new treatment method has to be tested on at least two species of animal – rodent and non-rodent – before it can enter the clinical phase and trials in healthy human volunteers.

7. Animal experiments benefit veterinary medicine too

Dogs, cats and rodents are no strangers to cataracts, all species of animal can develop cancer in various organs, and epilepsy is found in dogs, cats and rabbits. These are just a few of the diseases that people share with animals. Virtually every human disease exists in the same or a similar form in animals and is treated in essentially the same way. There are several areas of common ground between human and veterinary medicine. Many veterinary medicines contain the same API as their human counterpart. Thus, animal experiments also benefit other animals.

Animal experiments and COVID-19 vaccines
Animal experiments played a key role in enabling researchers to understand SARS-CoV-2 itself, the mechanisms by which it is transmitted and the safety and efficiency of the vaccines that have been produced to date, thus bringing us one step closer to the end of the COVID-19 pandemic.

8. Major progress thanks to animal experiments

Animal experiments are only permitted if they are essential for elucidating as yet unresolved questions. They are part of basic research and prescribed by law for the development of new medicines and treatments (preclinical research). The intention of animal experiments is not only to create specific applications, but also to generate knowledge that can be used to develop innovative medicines and therapies. Or in other words, studies and experiments involving animals increase our knowledge of the natural world. They help us gain a better understanding of diseases. Findings from animal experiments can be transferred to humans with sufficient certainty to be able to deduce principles of action and harmful effects. There can be no question that animal experiments make a major contribution to the development of new methods of medical treatment. For example, it is now possible to cure childhood leukaemia in 80 percent of cases thanks to animal experiments. The most recent example is the rapid and successful development of various COVID-19 vaccines.

9. Animal experiments reduce animal experiments

Research has not yet progressed to a point where it can dispense with animal experiments. Although it is possible to go a long way using computer models and cell cultures, while technologies such as organ-on-a-chip can be used to replicate simple processes, the complex processes that take place within an organism cannot (yet) be reproduced with the methods currently available. This is because even the processes that take place within a single cell are too complicated for a computer. Animal experiments are therefore still needed for the time being – partly to continuously improve them and to replace them at ever smaller intervals.