Biomedical research continues to rely on laboratory animals, both to conduct basic research and to be able to continue developing effective and safe medicines, vaccines and other treatments. Clinical research is based on the results of basic research. Furthermore, there are scientific questions that cannot be researched with alternative methods at present.
Animal experiments provide a greater degree of safety. Without them, it would be necessary, for example, to study medicinal products, whose effect had been investigated in cell cultures or with computer models, directly in humans. Studies of medicinal products are intended primarily to obtain information about effect and the behaviour of an active ingredient in a living organism that resembles a human being. For ethical reasons, it is not possible to expose human beings to the risk of these kinds of investigations. The risk of an undesirable effect from a substance is very high for humans if the substance has not been tested for innocuousness in animal experiments.
Only when adequate information about effect and innocuousness, supported by tests involving several animal species, has been gathered is it possible to draw reasonably secure conclusions with regard to the effect on humans. This does not represent an absolute guarantee for the safety of a substance in the human body, but it does protect human test subjects against unjustified, massive side-effects, with a high degree of probability.
Further: What doctor would risk causing life-threatening injury to a human when testing a new substance? What patients or volunteers would be willing to take a medicinal product whose safety and efficacy had not been previously tested in an organism, i.e., in an animal experiment,? These steps are spelled out in legislation for the protection of humans; they stipulate that new medicinal products and surgical treatments must first be tested on animals before they can be tried, under rigorous safety constraints, on humans. These globally applicable ethical principles of human medicine were established after World War Two (Nuremberg Code; now Declaration of Helsinki), to prevent the future conduct of experiments with humans, such as those performed in concentration camps in Nazi Germany.
Cell or tissue cultures allow only partial investigation of the effect of a medicinal product. In the development of medicines, these partial aspects are also studied with in vitro methods. This is, however, not sufficient: the body is a highly complex structure; the different organs, cells, metabolic or hormonal systems are connected by a myriad of "feedback loops". For the safety of the patients and for the development of better treatment methods, it is therefore vital that a medicine or a certain treatment is tested within the body itself. For example, the effect of a medicinal product on the heart may be different, if part of the active ingredient has been modified by the liver. Consequently, the investigation of substances in the living organism is indispensable.