The legal basis in Germany is the German Animal Welfare Law, and in Europe it is the European Union (EU) Directive 2010/63. These laws specify that the number of animal studies conducted must be kept to the absolute minimum required, and that animals can only be used in a study if its objectives cannot be achieved by other methods. Bayer also has to comply with the European guidelines and German Medicines Act. These laws require an active ingredient to be tested in animals before entering clinical trials.

Mainly rodents, particularly mice and rats. This is because their physiology is very similar to the human body. Regulatory authorities usually require studies in both rodents and non-rodents.