According to law, the safety of new products first needs to be investigated in animals before the products can be tested in humans. Besides this legal framework, there is of course also an ethical aspect which plays a big role in this debate.
For the development of new products, medicines or therapies, it is important to first investigate the underlying mechanisms of the disease. This is so called fundamental research. This research is mainly conducted in vitro but sometimes it is also done by means of an animal experiment because complex processes cannot always be simulated in a petri dish. At the end of the study, the experimental animal is usually euthanized in order to further investigate the tissues and organs. This last step is ethically impossible in humans.