Why animal testing is bad science.

Many people may assume that animal testing exists because it works — that it’s a necessary step to protect human health. But when you look at the evidence, a different picture emerges.

Despite decades of reliance on animal experiments, they remain poor indicators of what will happen in people. Around 9 in 10 new drugs that pass animal tests still fail in human trials[1] — usually because the animal data didn’t predict human responses.

And the cost of these failures is profound — both for the animals and for the human patients left waiting for real medical breakthroughs.

Here are 3 reasons why animal testing fails and how you can help shape a future where science protects people without harming animals.

Researchers artificially create conditions in primates, rats, mice and other animals, but these models cannot capture the true complexity of human illness. The results rarely translate to people[2].

Small differences in immune function, metabolism, genetics and organ biology can turn a “safe” result in rats, dogs or monkeys into a dangerous outcome in humans[3].

Real patients vary in age, diet, genetics, environment, and co-existing health conditions. These differences profoundly shape how people respond to medicines — yet animal tests erase this complexity[4].

Around half of all drug failures happen because treatments simply don’t work in humans. Another ~30% fail due to toxic effects animals failed to predict. This isn’t an occasional flaw — it’s a pattern that has persisted for decades[5].

Drug safety failures.

These high-profile cases show how often animal tests provide false reassurance:

• Vupanorsen, a cholesterol-targeting drug. Safe in rats and monkeys, but caused dose-dependent liver injury in humans, ending development in 2022[6].
• Ziritaxestat, a treatment for severe lung disease. Harmless in rat and dog studies yet halted in 2021 after unexpected excess mortality in human Phase 3 trials[7].
• BMS-986094, an antiviral for hepatitis C. Passed extensive animal toxicology tests but triggered fatal cardiac and renal failure in human volunteers, leading to immediate discontinuation[8].
• TGN1412, a drug developed for leukaemia and arthritis. It appeared safe in mice, rabbits, and monkeys, but when tested on healthy volunteers, it triggered a catastrophic immune reaction that caused multiple organ failure[9].

Even when drugs do make it through to market, animal testing has failed to protect people from harm:

• Thalidomide caused devastating birth defects in tens of thousands of babies despite being found safe in 10 strains of rats; 11 breeds of rabbit; 2 breeds of dog; 3 strains of hamsters; 8 species of primates; and various cats, armadillos, guinea pigs, pigs, and ferrets[10].
• Vioxx, used to treat pain and inflammation, was cleared in monkeys, rats, dogs, guinea pigs and rabbits yet went on to cause an estimated 60,000 excess deaths from heart attacks and strokes before it was withdrawn[11].
• Isuprel for the treatment of asthma caused over 3,500 deaths in Great Britain alone, despite safety in rats, guinea pigs, dogs and monkeys, all of whom had received doses far exceeding those administered in humans[12].

Even today, drugs like Ozempic — which sailed through animal trials — are revealing serious human side effects[13].

Biomedical research failures.

Animal-based data have been particularly poor predictors of drug success for multiple common diseases. Some of the most striking failures include:

• Alzheimer’s: After 30 years of “cures” in mouse models, more than 99 % of drugs have failed in people. Scientists now describe Alzheimer’s as one of the most striking failures in modern translational medicine, with decades of success in mice and rats producing no effective human therapy[14].
• Stroke: More than 1,000 treatments worked in animals, yet none have proven effective for people beyond existing clot-busting drugs[15].
• Parkinson’s disease: Decades of artificially induced Parkinsonism in rats and mice have delivered no cure, and animal models still cannot replicate critical non-motor symptoms seen in humans[16].
• Cancer: Billions have been spent targeting tumours in mice, yet these studies have not solved metastasis – the spread of cancer that kills most patients. Even the most promising anti-cancer therapies in mice and rats routinely fail in human trials[17].
• Sepsis: At least 150 drugs have succeeded in mice, yet none have helped humans, because their immune systems simply do not respond the way ours do[18].

Despite years of animal experimentation, over 90% of animal-based research never helps human patients[19]. Relying on animals in biomedical research has sent medical science down costly, misleading paths, delaying real breakthroughs that could have come from human-relevant research[20]. And despite being proven unreliable, billions of dollars continue to be invested.

Around the world, cutting-edge technologies are replacing outdated animal experiments with methods that are more accurate and directly relevant to humans. Known as New Approach Methodologies (NAMs), these innovations are already being used in regulatory testing, drug discovery and disease modelling[21].

Adopting human-relevant methods is not just about replacing animals — they redefine research, offering faster, more effective and more ethical pathways to understanding human health and disease.

This is modern science that is better for animals and better for people.