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New study questions value of animal tests

A new study has called into question the ability of animal tests to predict the safety of human drugs. The study, published in scientific journal Regulatory Toxicology and Pharmacology, should raise questions about the extent to which animal safety tests actually protect patients from the harmful effects of the medicines they take.

Researchers from Utrecht University in the Netherlands recently published their report as part of a larger project which is looking at the value of animal studies in drug development. They analysed animal data used to evaluate the safety of 43 drugs in order to determine how predictive the studies were of human side effects. Out of 93 serious adverse reactions prompting action by the regulatory authorities – such as changes to the side effects listed on the packet but also withdrawal of the drug from the market - only 19% could have been predicted based on the animal tests done before the drugs were released onto the market.

It is sometimes claimed that animal tests are not designed to predict relatively rare human side effects to medicine. However, the authors point out that the animals were given high doses for prolonged periods of time and the tests should, therefore, have been able to detect the kinds of serious side effects seen in these drugs. 

This study builds on the results of two other large-scale studies, one conducted in Japan in 1995 which showed that only 23% of effects seen in animals were seen in humans (2) and another in 2000 that showed that rodent safety studies only predicted 43% of human reactions (3). 

The authors of this latest study concluded that “Although the pharmaceutical industry and regulatory authorities rely on animal studies to predict the safety and efficacy of new therapeutics in humans, it is striking that few attempts have been made to demonstrate this predictive ability”…

“Yet, our study suggests that for the majority of drugs animal data in these plans will be redundant because animal data do not appear to be an optimal tool for prospectively assessing risk in humans.” (4).


1. The ability of animal studies to detect serious post marketing adverse events is limited. Regulatory Toxicology and Pharmacology 64, 345–349. 2012

2. Predictability of clinical adverse reactions of drugs by general pharmacology studies. Journal of Toxicological Sciences 20, 77–92. 1995.

3. Concordance of the toxicity of pharmaceuticals in humans and in animals. Regulatory Toxicology and Pharmacology 32, 56–67. 2000.

4. Plans=Risk management plans that identify how the drug should be monitored for adverse reactions in patients once released onto the market