The use of animals in the search for new drugs is not always reliable. Physiological differences between species can produce various results. There have been major medical break throughs without the aid of animals. X-rays were developed without the use of animals, as well as the vaccine for yellow fever. Penicillin may have never gotten past preliminary testing if it were tested on guinea pigs because the drug is fatal for the rodents. Penicillin was also discovered without the use of animals. Salicylates (aspirin) causes malformations in rats, but not in humans. Since 1986, the National Cancer Institute (NCI) has reduced the number of animals used in experiments from 6 million to fewer than 300,000 per year.(Living Planet Press, 1990) The NCI's anti-tumor drug discovery program uses human tumor cells instead of animals and has proven to be faster, more dependable and more cost effective. Tissue cultures for AIDS research has been used to isolate, identify and concentrate the AIDS virus and is rapidly being used to test new drugs. .
Some drugs that have been extensively tested on animals have proven to be unsuccessful and even harmful to humans. Thalidomide was tested on animals for 6 years before being marketed. Zomax, a common painkiller was withdrawn after 14 deaths and hundreds of life threatening allergic reactions. .
In Britain a drug called Oparin, which was used to treat arthritis, was withdrawn from the market. This drug was promoted by the drug company Eli Lilly as having the potential to cure arthritis on the basis of curing artificially induced arthritis in rats. When it came to treat humans, it didn't cure it. In fact, Oparin killed many people. It killed them because the drug was not metabolized in the body very rapidly in elder patients.(Micheal Fox, 1990) .
Because animals react so differently than humans, some dangerous drugs slip through the most extensive animal experiments and potentially useful ones may be lost.