Before people
New treatments are first studied in the laboratory and, where required, in animals. Only promising and apparently safe ones move on to trials in people.
The phases
Phase I
A small group — often 20 to 80 people — to study safety, side effects and how the body handles the treatment.
Phase II
A larger group, often several hundred, to see whether it works and to keep studying safety.
Phase III
Large groups, often 1,000 to 3,000 people or more, to confirm it works, watch for side effects and compare it with standard treatment.
Phase IV
After approval, studies continue in the wider population to track long-term benefits and rare side effects.
Taking part
Trials are voluntary and follow ethics rules: participants are told the purpose, risks and possible benefits before giving informed consent, and can leave at any time.
Sources
- Clinical Trials — MedlinePlus — U.S. National Library of Medicine. Checked 2026-09-26.
- What Are Clinical Trials and Studies? — National Institute on Aging (NIH). Checked 2026-09-26.
Editorial update: 2026-09-26.
Medical disclaimer: this is a source-linked educational summary, not individual medical advice, diagnosis, prescription or interpretation of personal results. For severe or rapidly worsening symptoms, call 115.
Antopeloni — plain-language health education from public sources, part of the ZIBADIS network founded by Masoud Moghaddam.
