All studies achieve only a relative degree of safety, and the aim is to assess risks as fully as possible in order to develop a medicine that is as safe as possible. However, absolute safety can never be guaranteed.
Undesirable effects can also be influenced by the life style. For example, patients who consume excessive amounts of alcohol may experience different side-effects than people who drink little or no alcohol at all. Furthermore, possible interactions with other medicines or a patient’s other illnesses need to be considered.
The genetic diversity of patients likewise plays a role. Metabolic activity varies from human to human and an active ingredient is processed differently as a result of genetic differences. This may be the cause of rare side-effects. Thus, it may happen in an individual case that new side-effects not observed in the clinical studies are reported, even with medicines already registered.
The safety tests in animal experiments are only a first of many safety tests carried out before a medicine is registered, and they are followed by further similar tests with humans in clinical studies (see also the individual phases). Firstly, the animal experiment is used to investigate the principle of action, in order to determine whether a medicinal product is in fact effective and if so, how. Secondly, whether an active ingredient is safe enough for use in humans is evaluated.
The active ingredient will only be tested with caution in humans after this test phase, and if it proves to be effective and safe in the subsequent clinical trials with healthy persons and/or patients, an application can be filed to register the active ingredient as a medicinal product. This process normally takes four years.