The long path to a medicine

4. Clinical trials in humans

Only drug candidates that have proved safe and effective in animals are approved for trials in humans. The clinical trial is a lengthy and organizationally challenging process. In a first step, the results obtained for example in animal studies on tolerability, absorption, distribution, metabolism and elimination of drug candidates are verified in a limited number of healthy human subjects (Phase I trials). These are followed by Phase II trials in a manageable number of patients, which yield information in particular about efficacy, side effects and the appropriate dose of the substance. The findings are verified in Phase III trials involving thousands of patients. Thanks to the large number of participants, rare side effects can also picked up in these trials. In parallel with the clinical trials in humans, further studies are carried out in animals, with which side effects during long-term use or impairment of fertility can be established, for example.