Study types · reviewed 2026-08-17
Observational vs interventional studies
How ClinicalTrials.gov StudyType differs when researchers assign a treatment versus when they only measure what already happens.
Interventional
The protocol assigns participants to a drug, device, procedure, or behavioral program (sometimes by randomization). Phase 1–4 labels usually apply to drug or biologic interventional studies.
Observational
Researchers collect data on people receiving care, or follow a cohort, without assigning the experimental intervention as the study treatment. Registries, natural-history studies, and some biomarker studies are observational. They still require consent when they are research.
Why the distinction matters to you
If you are looking for access to an investigational product, an observational record will not provide it. If you want to contribute data with fewer extra procedures, observational studies may fit. Always read StudyType on the NCT page. PlainTrials surfaces that field on trial cards.