In order to test toxicological effects of potential new pharmaceuticals, a wide range of trials is carried out. Phase 0 (human microdosing) and phase 1 trials are also known as first-in-human trials, with small numbers of patients (typically 20 to 80) that receive the API in small capsules.

The application is similar to preclinical trials but the substances must have pass these successfully, in order to continue to phase 0 and phase 1. All compounds need to be treated according to FDA regulations, i.e. FDA approved contact surfaces and proven sterility. The duration of the study might be up to a year.