New research paper shows: 91% of potential drugs fail despite successful animal experiments

A new scientific study led by the German organisation Doctors Against Animal Experiments (DAAE) shows that, although an increasing number of animal experiments have been conducted, drug development has not become more successful at producing effective and safe medicines for humans over the past half-century. During the 2000s and 2010s, an average of approximately 91% of drug candidates failed in human clinical trials despite having successfully passed preclinical animal testing. In around 77% of these failures, biological factors – such as insufficient efficacy or inadequate safety – were decisive. These are precisely the factors that animal experiments are intended to predict. Both figures demonstrate the systematic failure of animal testing and the urgent need for human-relevant, non-animal methods.

Drug development involves multiple stages. Drug candidates may be tested in clinical trials involving human volunteers and patients only after they have successfully completed extensive preclinical testing, particularly animal experiments assessing their safety, efficacy and pharmacological properties. Nevertheless, the vast majority of drug candidates subsequently fail in human clinical trials. DAAE has long criticised the limited translatability of results from animal studies and has therefore systematically investigated failure rates and causes for drug failure in clinical drug development from the 1960s to 2017.

The results are summarised in the new publication, Need for NAMs: A systematic evidence synthesis revealing over half a century of drug development failure, published on 21 July 2026 in the international NAM Journal. The journal focuses on modern, non-animal research methods known as New Approach Methodologies (NAMs).

“For decades, researchers have claimed that animal experiments are a necessary and reliable basis for developing new medicines. However, our systematic analysis shows that the situation has not improved – it has actually become worse,” says Dr Dilyana Filipova, Scientific Officer at DAAE and one of the study’s two lead authors.

13 researchers, six decades of data

The study is the first systematic evidence synthesis to bring together clinical failure rates over almost six decades while also distinguishing between biological and non-biological causes. A total of 13 scientists and experts from universities and industry with expertise in non-animal methods contributed to the study. The international team comprises experts from Germany, the Netherlands, Australia, the United Kingdom, the United States and Denmark.

DAAE played a leading role in the study. Dr Dilyana Filipova and Dr Tamara Zietek, Chief Scientific Officer at DAAE, are the lead authors. Scientific Officers Leyla Fox and Dr Gaby Neumann are also members of the author team. The co-authors also include Dr Wolfgang Boomgaarden, founder of the innovative company PharmaInformatic and recipient of the 2021 Herbert Stiller Research Prize for his work on computer-based, non-animal methods for drug development.

91% of drug candidates fail after animal testing

The international author team analysed data on the clinical development of medicines over almost six decades. The failure rate increased in every successive decade from the 1980s onwards. During the 2000s and 2010s, an average of approximately 91% of drug candidates that had successfully completed the preclinical phase, including animal testing, failed in human clinical trials.

The analysis therefore confirms the frequently cited estimate that nine out of ten drug candidates ultimately fail to become an approved medicine for human use despite successful preclinical animal testing. At the same time, it is the first study to systematically examine how these failure rates developed over six decades.

“If the predictive capacity of preclinical research were genuinely sufficient, the success rate would have to increase over time. The fact that this has not occurred fundamentally calls into question the validity of the prevailing development model,” says Filipova.

Biological factors are central

Approximately 77% of failed drug candidates failed because of biological factors, including insufficient efficacy, unexpected adverse effects or inadequate safety. These are characteristics that are assessed particularly in late-stage preclinical animal studies before a drug candidate is tested in humans.

For the first time, the study systematically distinguishes between biological and non-biological causes, including strategic, economic and commercial factors. The results show that most failures cannot be attributed solely to corporate decisions; rather, they are associated with biological problems that animal experiments frequently appear unable to predict reliably.

“Our analysis makes it clear that animal experiments often fail to identify the risks that are decisive for human use. A drug candidate may appear safe and effective in animals, yet prove ineffective in humans or cause serious adverse effects,” Filipova explains.

Modern research instead of animal testing

The findings underscore the urgent need to fundamentally reform drug development. Rather than relying on animal experiments, greater use must be made of methods that directly model human biology. In recent years, regulatory authorities and pharmaceutical companies worldwide have shown growing interest in NAMs because of the potential for more reliable and applicable predictions to humans.

NAMs can capture human disease mechanisms and drug responses more precisely than animal experiments. A regulatory shift is also emerging: roadmaps and strategies developed by the US Food and Drug Administration, the UK Government and the European Commission aim to advance the development, validation and application of NAMs and gradually replace animal testing. NAMs must therefore become the central foundation of modern, human-relevant pharmaceutical research.

“We need a paradigm shift: away from animal experiments that perpetuate the biological differences between animals and humans, and towards precise methods based on human cells, tissues and disease processes,” Filipova urges. “The available data show that this transition must happen not at some point in the future, but now – in the interests of patients, scientific quality and animals.”

Reference

Filipova D. et al. Need for NAMs: A systematic evidence synthesis revealing over half a century of drug development failure. NAM Journal. 2026; 2:100119. Read the publication