As per ICH-GCP Guidelines, Investigator is “A person responsible for the conduct of the clinical trial at a trial site. If a trial is conducted by a team of individuals at a trial site, the investigator is the responsible leader of the team and may be called the principal investigator.”

A researcher involved in a clinical study. Related terms include Site principal investigator, Site sub-investigator, Study chair, Study director, and Study principal investigator.

A medical professional, usually a physician but may also be a nurse, pharmacist or other health care professional, under whose direction an investigational drug is administered or dispensed. A principal investigator is responsible for the overall conduct of the clinical trial at his/her site.