The aim of this phase is to study the security and toxicity of the new medicine. During this phase, the secondary effects that the drug may have on the health of the patient are considered (e.g. blood pressure rise).
The number of participants in this phase is small and in the case of adults these are all healthy volunteers. In paediatric clinical trials, however, phase 1 only includes patients because it is considered unethical to expose a healthy child to any drug.
The number of patients in phase 1 range between 20-100.