Clinical trials without the alphabet soup.

Preclinical research

Before broad human testing, researchers may study a compound in cells, tissues, or animals. This can reveal mechanisms and obvious hazards, but it cannot prove a treatment works safely in people.

Phase 1: first questions in people

Phase 1 generally focuses on safety, tolerability, and what the body does with a drug. These studies are often small. They may include healthy volunteers or people with a condition, depending on the research.

Phase 2: does the signal hold up?

Phase 2 studies explore effectiveness, dose selection, and continued safety in people with the target condition. Encouraging Phase 2 results still need confirmation.

Phase 3: larger confirmation

Phase 3 trials are usually larger and designed to confirm benefits and characterize harms in the population intended for a potential label. A Phase 3 trial can fail, be delayed, or answer only a narrow question.

FDA review

A sponsor submits a formal application with clinical, manufacturing, and labeling information. FDA review is separate from trial registration and from a company announcing topline results.

Approval versus off-label use

Approval covers the product and uses described in its label. Licensed clinicians may sometimes prescribe an approved medicine off-label, but that does not make the off-label use FDA approved. This site does not recommend treatment choices.

Why early results can be misleading

• Small studies can exaggerate effects by chance.
• A press release may arrive before peer review or complete data.
• Dropouts and missing data can change the story.
• A surrogate endpoint may not predict how people feel or function.
• Rare harms often require larger or longer studies to detect.

How to read a trial update

• Check whether the result is registered, complete, and peer reviewed.
• Look for the primary endpoint—not only favorable secondary findings.
• Compare absolute results, adverse events, and discontinuations.
• Ask whether the comparison group and population fit the claim.
• Treat estimated completion dates as estimates, not promises.

Sources for this guide

These official and educational sources support the general regulatory and research concepts explained on this page. For a specific medicine, use the fact sheet's product-level sources.

1. 1

   fdaFDA: the drug development process

   Official overview of preclinical research, clinical research, FDA review, and post-market monitoring.

2. 2

   clinical trialsClinicalTrials.gov: how to read a study record

   Explains how to interpret recruitment status, endpoints, enrollment, results, and record history.

3. 3

   nihNIH: clinical trials and you — the basics

   Plain-English NIH overview of trial phases, participant protections, and what each phase can answer.

4. 4

   nihNIH: understanding clinical studies

   Explains why study design, comparators, and endpoints matter when interpreting findings.