They discovered, for instance, that chemically-induced cancer of the colon in rats was not relevant to our understanding, diagnosis and treatment of human colon cancer. The problem is that artificially induced disease in animals is never identical to the naturally arising disorder in people, making animal research a logically flawed process. Yet doctors have known for more than a century that human disease can take an entirely different form in animals. The writer explained that most human cancers behave differently to the artificially produced animal model and concluded that it is the study of human patients that will ultimately yield relevant results. With such differences tests on animals can be either worthless or positively dangerous because they provide a false sense of security.
Recent examples are the heart drugs encainide and flecainide.
Approved in 1987 following the usual animal tests, the drugs may have caused as many as 3,000 human fatalities. In the case of Oraflex, unforeseen effects actually led to the drug's withdrawal from use. There were no apparent adverse effects on survival. The failure of animal tests to warn against toxic hazards is not unusual. All the drugs were animal-tested in accordance with FDA guidelines.