The main purpose of a phase 1 or first in human trial is to assess whether a new treatment is safe in humans.

They are typically carried out on a small number of healthy adults in a carefully controlled clinical environment.

Before a phase 1 trial can be started, clinical trial authorization (CTA) must be gained from a regulatory authority, such as the US Food and Drug Administration (FDA), the European Medicines Agency (EMA), or a national regulatory authority (NRA).

A trial must also receive ethical approval, for example from an institutional review board or research ethics committee associated with a particular research institution or from a national research ethics committee.

As regulatory authorities have different requirements, a decision needs to be made during pre-clinical development on where a phase 1 study will be conducted, so that the trial can be designed to collect the appropriate data.