Can Medical Research on Animals be Justified?

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We see the headlines every day: “New miracle drug cures xxx disease in mice.” Rarely do we see follow-up stories touting the drug’s effectiveness in humans.

That’s because 92 percent of all drugs that enter clinical trials following extensive animal testing fail to achieve FDA approval, either because they don’t work for people or they are dangerous. Of the 8 percent overall that are approved, half are withdrawn or relabeled due to severe or lethal adverse effects not detected during animal testing. Vioxx and Rezulin are just two of many drugs that looked safe in animals but proved dangerous to humans.

There are numerous reasons why animal tests can’t reliably predict human outcomes, including species differences in anatomy, organ structure and function, gene expression, drug and chemical absorption and metabolism, and mechanisms of DNA repair. Simply put, animal models are not good predictors for what will work in humans.

Entire fields of science are failing because of the difficulty of translating animal data to effective human treatments. For example, all of more than 80 preventive and therapeutic HIV/AIDS vaccines developed in nonhuman primates have failed in human trials. Of 700 treatments for stroke developed in animals, all of the 150 tested in humans failed. Despite decades of expensive studies, the field of cancer immunology has failed to produce even one successful therapeutic cancer vaccine.

While many dangerous drugs come to market because they looked safe in animals, the reverse is also true. There are many useful, safe drugs such as aspirin that were developed decades ago--before the requirement for animal testing was established. If scientists had first tested aspirin in animals, for example, that indispensable drug never would have been approved because aspirin was later found to cause birth defects in mice, rats, guinea pigs, rabbits, cats, dogs, and monkeys. Penicillin and acetaminophen are two other examples of widely used beneficial drugs that would not survive animal testing because they are toxic for some species.

In other cases, life-saving information about human health has been withheld from the public because of animal tests. For example, in the early 1940s, human clinical investigation strongly indicated that asbestos causes cancer. Yet, animal tests repeatedly failed to demonstrate this, and proper workplace precautions were not instituted in the United States until decades later.

Tobacco is another example. Although smoking’s link to lung cancer first became evident from two landmark epidemiological studies in 1950, legions of animal studies failed to reflect human sensitivity to tobacco exposure. These studies delayed public health warnings against cigarette smoking for years, contributing to untold numbers of preventable human deaths.