Each drug must undergo a Phase I - III of clinical evaluation prior to its introduction into standard medical practice.
Phase I: If you are in a Phase I of a clinical trial, it means that it usually concerns the first time administration of the drug under research to humans. These trials are attended by only a small number of healthy volunteers around the world (approximately 15-30). At this stage, it is determined whether the new treatment is safe and how it affects individual organs of the body. The dose which is tolerated by the body, and does not cause significant side effects, is measured. In rare cases, the drug subjected to research is administered not only to healthy volunteers, but also eg to oncology patients.
Phase II: The substance is first administered to a small number of patients with a target disease. The therapeutic effects on the human organism are verified, adequate dosing is sought, additional data on the effect of the potential drug are collected, eg for what type of tumour it is suitable. This phase of evaluation is attended by a maximum of hundreds of patients.
Phase III: This concerns already large clinical trials involving up to thousands of patients in different hospitals around the world. The main goal of Phase III trials is to find out whether the new treatment is better or at least as good as the one used as standard. These are mostly randomized (randomly allocated), or eventually placebo-controlled trials.
Phase IV: It is a so-called Post-Authorization Trial. Clinical trials continue even after approval, the drug registration. Their goal is to gain further new knowledge of the side effects of the drug.