Animal experiments have been the subject of controversial discussions for many years now. Considering both ethical and scientific arguments, opinions could not be more di-vided. Advocates of animal experiments do not get tired of emphasizing medical pro-gress would not be possible without experimenting on animals, while critics have scien-tifically proven animal experiments include an incalculable risk and are a dead-end field for humans.

A selection of typical arguments for and against animal experiments will be presented here. A closer look will reveal there is no scientific foundation for arguments supporting animal experiments, and alleged benefits or a “lack of alternatives” is just pretext to keep the system running.

Arguments supporting animal experiments

1. Better to conduct research on animals than on humans?

Advocates of animal experiments often pose the question, “Would you prefer testing directly on humans?” This question creates a scenario that does not exist in reality. The point is not to choose whether to test a potentially toxic substance on humans directly or on animals first. The point is animal models are unsuited to reliably assess how hu-mans may respond to the same substance, be it, for instance, the effects of new drugs on the human body, or the effectiveness of new treatment methods.

2. No medical progress without animal experiments?

Advocates supporting animal experiments will often say, “Without animal experiments there would not be any medical progress and we would not have effective treatment methods,” or, “Medicine would get stuck in its current state.” This leads to the impres-sion animal experiments are indispensable for successful biomedical research.

In fact, in all medical fields experiments are conducted on animals every day, whether it is cancer research, exploring cardiac and metabolic diseases, or brain research. And these animal experiments are typically justified claiming potential usefulness for pa-tients. But does this also mean we owe our modern treatment methods to research on animals?

The fact animal experiments have been conducted in the past does not mean medical milestones could only be achieved this way. We do not know where medicine would be standing today if experimenting on animals had been prohibited 100 or 150 years ago. We probably would have advanced a lot further as their false results impede medical progress. If animal experiments were prohibited, other methods (e.g., in the field of in vitro), clinical research, and the prevention of diseases would be the focus of attention and thus lead to an improvement in health status. The conduction of animal experiments in the past is therefore neither proof they are necessary, nor do they say anything about the future of medicine.

Furthermore, the significance of animal experiments for earlier medical achievements have regularly been overstated. Numerous discoveries of great medical significance have been achieved without animals, and many times, they were “reproduced” in animal experiments afterward. And then it was often claimed the animal experiment was responsible for the major breakthrough. A variety of medical achievements are actually rooted in animal-free research. For example, aspirin was discovered without animal experiments in the middle of the 19th century. If the subsequent animal experiment had been trusted, this beneficial drug would have been kept from us as it is harmful and even lethal for some animals.  

3. Animal experiments make drugs and substances safe for us?

Before a new drug or chemical substance is released to the market, it is first tested on animals and then, in clinical studies, on humans. This is supposed to ensure humans will not be harmed. Yet it is fatal to draw conclusions based on the effects the drug or substance has on animals, as numerous everyday-life examples demonstrate. Chocolate, for instance, is tasty for us humans but toxic for dogs and cats due to the included theobromine. Humans better refrain from eating death cups as they are lethal for us. Rabbits, in contrast, can eat them without problems. Paracetamol is an effective painkiller for humans but toxic for cats. Animal experiments create a false sense of safety, which can have fatal consequences for humans.

4. There are not enough “alternatives?”

It should be noted the word “alternatives” is in quote marks because the word implies animal experiments are technically a beneficial method that only needs to be replaced. However, the issue is not a 1:1 replacement of animal experiments with animal-free methods. Rather, validity, i.e., the scientific informative value of a method, needs to become the focus of attention. Recognizing this makes it clear animal experiments are primarily based on belief rather than on a reliable scientific foundation. Furthermore, the term “alternative” includes animal-free as well as pain-reducing methods that do not question animal experiments per se.

Researchers experimenting on animals often argue to conduct only experiments that are absolutely necessary and to not have an appropriate replacement method available. They thus convey a “lack of alternatives,” which has to be considered a system error for the reasons outlined above. If we focus on the goal of developing and using research methods that successfully advance medical progress and provide reliable results for us humans, it becomes obvious right away we need a paradigm shift toward modern hu-man-based methods. Our NAT Database (Non-Animal Technologies) includes a selec-tion of fantastic animal-free methods.

Arguments against animal experiments

1. Humans are not mice - animal experiments cannot be translated to humans

Even individual humans are incomparable. For example, age, sex, and lifestyle, among other factors, play a significant role in how the human body responds to drugs. Furthermore, humans and animals differ from each other just as individual animal species do, regarding physique, organ function, metabolism, and diet. Considering these differences, how could the results found in animals possibly be translated to humans?

Looking at the carcinogenic effect of substances, mice and rats show a match of only 50 percent (1). Another study revealed great differences in the immune system’s response of humans and mice to blunt trauma, burns, or sepsis. It was shown humans respond to inflammation much more strongly, and to some extend, the body’s response can last up to half a year. The response of a mouse’s immune system decreased after only a few days (2).

Research on Alzheimer’s disease, which relies on “animal models,” misleads again and again. There are numerous treatment options that appeared to be successful in animals. However, not a single drug has come out of them to heal the disease in humans or halt its progress (3). Research on human mini-brains at Ruhr University Bochum has revealed a mechanism that probably explains how the nerve cells in patients with Alzheimer’s disease die (4). This finding, which is relevant to humans, is based on research free of animal experiments. Even many more animal experiments would not have been able to conclude such an important finding.

 At the University Hospital Charité in Berlin researchers have found a drug for Leigh syndrome, which used to be an incurable disease of the central nervous system. They did not find the drug through animal experiments but through modern, patient-specific research. A 15-year-old patient who was already paralyzed, unconscious, and had to be artificially respirated was treated with this new method. Out of the patient’s cells, the researchers first obtained induced pluripotent stem cells that were then converted into neuronal cells. That way, new cells of the central nervous system developed which were used to test potentially effective drugs. One drug already approved for another disease turned out to be successful.

In the researchers’ statement it says, “Spectacular about it was not only the successful treatment. All the animal experiments had failed to find a treatment option for Leigh syndrome (5).” Once again it becomes obvious how unsuitable animal experiments are with regard to medical progress and how they even block it. 

2. Over 90 percent of the medicine tested on animals fail in humans

The scientific facts are clear: Over 90 percent of all drugs proven effective in animal experiments fail in humans. They either show no effect at all or trigger strong side effects that can even lead to death (6, 7, 8).

Medical scandals have also dramatically shown tests on animals do not automatically mean being safe for humans. One example is TGN1412, a potential remedy for multiple sclerosis, which was tested on humans in the clinical phase 1 in 2006 for the first time and led to multiple-organ failure in six human subjects. Another example is the therapeutic drug Bia 10-2472 for chronic pain. After being administered to humans in 2016, five subjects experienced severe neurological damage, and one person died.

Even after releasing drugs to the market, severe damage not detected in animal experiments can often occur in humans. Of the about 10 percent of the drugs that make it to the market, about one third will be removed or labeled with a warning (9). Examples are the rheumatism drug Vioxx; the heart drug Trasylol; the blood lipid-lowering Lipobay or Zinbryta, a remedy for multiple sclerosis.

According to a study of the Hannover Medical School, there are approximately 58,000 fatalities caused by the incorrect intake or undesirable side effects of drugs. This number only includes patients dying in the hospitals’ internal medicine departments. Not considered are patients in other departments, outpatients, people dying at home, or patients with chronic long-term consequences caused by the side effects of drugs.

3. Animals are not suitable “models” for humans

It has become standard to use animals as so-called “models” for exploring human diseases. The term “animal model” suggests an appropriate animal is available for every human disease.

And indeed, for almost every question or disease there is a an “animal model.” But are they suitable representations of humans?

Whether it is cancer, diabetes, Alzheimer’s disease, heart diseases, or depression: In these “animal models,” the human diseases are reduced to their symptoms and induced artificially.

For instance, cancer and Alzheimer’s disease are triggered in mice through gene manipulation; a stroke is imitated by clogging a brain artery in rats or mice; and in depression research, rats are forced to swim in an unescapable water container until exhaustion.

These “animal models” are unnaturally constructed far away from reality and are in no way suited to explore the complex connections in the development of human diseases as they completely ignore critical factors, such as age, sex, genetics, diet, stress, and environmental aspects. It is therefore not surprising animal experiments do not advance medical progress but rather impede it.

4. Animal experiments as a lottery game - results are not reproducible

In an attempt to reproduce, i.e., repeat, results, animal experiments are conducted under what the system considers standard conditions. Therefore, animals of the same age, sex, and weight are used. The decisions on what to feed and how to house animals also follow constant laboratory conditions. Nonetheless, one and the same experiment can lead to completely different results. This is partially due to the fact that each animal is an individual and the factors influencing the development of diseases are ignored in those artificial lab conditions. How the animals are handled can additionally distort the results, e.g., through the level of stress they experience. Typically rats and mice, inter alia, are kept in a sterile environment in small plastic boxes with some bedding and the boxes being stacked on each other. It was shown animals are willing to work for the opportunity to experience an interesting environment, build nests, or socialize with their conspecifics. Rats in a sterile environment have smaller brains than animals in a diverse environment, and rats kept secluded from others try more frequently to escape their cages than rats living in groups. The behavioral researcher Dr. Jonathan Balcombe of the Physicians Committee for Responsible Medicine (PCRM) in Washington drew these conclusions after evaluating 200 publications on the housing conditions of rodents (10).

No other scientific method is as unreliable and unpredictable as animal experiments. We can only know after testing the substance on humans if an animal - and if so, which animal species - responds to that substance in the same way as the human body. Animal experiments are consequently a lottery game regarding the translation to humans, coming with incalculable risks for humans and meaning a painful, useless death for the animals.

5. Animals experiments inhibit medical progress

As has been historically proven, animal experiments are not suitable to develop reliable and effective treatment options for humans. For instance, penicillin, aspirin, and paracetamol were discovered without animal experiments about 100 years ago and have become indispensable in modern medicine.

Given today’s requirement to test all potential drugs on a number of animals to ensure their effectiveness and safety, we would not have all these beneficial drugs and those low in side effects. Based on animal experiments, they would have never made it to the market. While aspirin has no negative impact on unborn human babies, it leads to deformation in unborn cats, dogs, monkeys, mice, rabbits, and rats (11). Penicillin is lethal for guinea pigs and rabbits, yet is life-saving for humans (12). Paracetamol causes cancer in rodents and is poisonous for cats.

As long as medical research keeps using animal experiments as its gold standard, effective drugs and treatment options will continue to be kept from us, because they will be removed due to misleading animal experiments. At the same time, it can be assumed humans will continue to be victims of the side effects of drugs that appear to be safe in animal experiments but do not hold up in reality.

Animal experiments therefore are not only unethical toward animals but also toward patients who are exposed to risks or kept from treatment options due to misleading results in animal experiments.

If we do not fully distance ourselves from animal experiments, medical progress will continue to be blocked. Precious medical findings do not exist because of animal experiments but, inter alia, due to findings gained from human population studies and human-based research methods.

 6. “Alternative methods”: wide range of animal-free research

Why is the term “alternative methods” in quote marks? Because it suggests animal experiments can simply be replaced and do not need to be questioned as a method. You can read more here >>

Animal experiments are not only unethical but also completely outdated. In our modern age there are a variety of animal-free research methods, such as multi-organ chips, epidemiological research, or computer simulations that provide fantastic and - with regard to the translation to the human body - reliable results. Our ‘Database on Non-Animal Technologies’ includes thousands of modern animal-free methods.

There are many factors keeping the field of animal experiments going.

Treibende Motoren für den Beibehalt des Systems Tierversuchs gibt es viele:

1. Dogma

Animal experiments have been established as a “method of choice” in science since the middle of the 19th century. Only what can be demonstrated in animal experiments counts as scientifically proven. This dogma not only exists in the heads of many re-searchers but also in biomedical science programs and in a variety of laws. A funda-mental paradigm shift will be necessary to break up this dogma and to not longer con-sider animal experiments as the gold standard.

2. Career opportunities through animal experiments

Young scientists will be indoctrinated right at the beginning of their career, and often this indoctrination already starts in their college classes. Exercises using animals are typically a fixed component for students, and those who question the system either cannot continue their degree or face many obstacles extremely hard to overcome. 

Following the motto “publish or perish,” scientists are under enormous pressure to pub-lish their findings in renowned scientific journals of high impact. Only through such pub-lications may they increase their reputation. And since many scientific journals of high impact mainly publish animal experiments, it is the easiest way to have a career. The more a researcher publishes, the more subsidies they receive and can then use for more animal experiments in order to publish even more. It is a self-sustaining system.

3. Financial support

Research relying on animal experiments is subsidized with billions of euros in Germany alone, and that money mainly comes from tax revenue. Given less than one percent of the subsidies goes to animal-free research, while the rest supports animal experiments, it is not surprising career and earning opportunities are significantly better in research using animal experiments. Those who devote themselves to modern animal-free re-search instead receive little financial attention in spite of all the medical-scientific bene-fits this kind of research entails.

4. Lucrative business

Gigantic branches of the industry make money in the field of animal experiments. Breeders offer animals “produced” for specific experimental purposes that can be pur-chased as if out of a catalogue. A gene-manipulated mouse can cost up to 80,000 eu-ros (13). Laboratory suppliers offer cages and other equipment, and the experimenters themselves enjoy immense subsidies for their experiments. Continuing animal experi-ments therefore is not based on scientific necessity. Rather, numerous people profiting from the system want to keep this extremely lucrative business worth billions of euros going.

5. Liability of pharmaceutical companies

Customer safety is the typical argument given to hold on to animal experiments. Ignor-ing the fact such experiments produce misleading and dangerous results for humans, they protect companies when humans are harmed, as companies can refer to the con-duction of the legally required animal experiments and thus reduce their risk of liability. It is a mere alibi function at the cost of humans and animals.

Conclusion

Without any solid scientific foundation, the system of animal experiments has estab-lished itself in our society. Considering the ethical aspects and the great danger for us humans coming from research based on animal experiments, a rejection of the system has long been overdue. Animal experiments need to be abolished in order to make room for sophisticated and diverse animal-free research methods.

08/03/2021
Updated 14/04/2025
Dipl. Biol. Silke Strittmatter, biologist

References

1. Di Carlo FJ. Drug Metabolism Reviews 1984; 15:409-413
2. Seok J et al. Genomic responses in mouse models poorly mimic human inflammatory diseases. PNAS 2013; 110(9):3507–3512
3. Langley GR. Considering a new paradigm for Alzheimer´s disease research. Drug Discovery Today 2014; 19(8): 1114-1124
4. Ruhr-Uni-Bochum. Alzheimer im Mini-Gehirn, 30/04/2019 [accessed 07/03/2021]
5. Gesundheitsstadt Berlin GmbH. Stammzellen statt Tierversuche: Charité-Forscher finden erstmals Medikament gegen das unheilbare Leigh Syndrom, 02.03.2021 [accessed 07/03/2021]
6. Clinical development success rates 2006-2015. BIO, Biomedtracker, Amplion 2016
7. Clinical development success rates 2011-2020. BIO, Informa, QLS Advisor 2021
8. Why are clinical development success rates falling. Biomedtracker Citeline 29.04.2024
9. Downing NS et al. Postmarket safety events among novel therapeutics approved by US Food and Drug Administration between 2001 and 2010. JAMA 2017; 317(18):1854-186
10. Balcombe J. Laboratory environments and rodents' behavioral needs: A review. Laboratory Animals 2006; 40(3):217-235
11. Hartung T. Per aspirin ad astra. ATLA 2009; (37):45-47
12. Doctors Against Animal Experiments: 1929 – Penicillin, 03/09/2019
13. NBC News. Mice play a critical role in medical research, 03/06/2006 [accessed 07/03/2021]