What a clinical trial is
A clinical trial is a carefully planned study in people. It answers a specific question, such as whether a new medicine lowers blood pressure more than an existing one, or whether a device helps people sleep. Every trial follows a written plan, called a protocol, that sets out who can join, what happens at each visit and how the answer will be measured.
Not every study is a trial of a treatment. Observational studies give no treatment at all; they follow people’s health and record what happens. Both kinds need volunteers.
The four phases
New medicines move through testing in stages. Each one only starts once the stage before it has shown the treatment is safe enough, and useful enough, to go further.
- 1
Phase 1
A small group, often healthy volunteers, receives a new treatment for the first time. The aim is to learn whether it is safe and what dose to use.
- 2
Phase 2
A larger group who have the condition takes part. The study looks at whether the treatment works and keeps watching for side effects.
- 3
Phase 3
Many more people, often at sites across the country, so the new treatment can be compared with the one already in use.
- 4
Phase 4
After approval, studies keep following people who use the treatment, to catch anything rare or long term.
Randomisation and placebo
In many trials a computer assigns each volunteer to a group by chance. This is randomisation, and it keeps the groups alike, so a difference at the end can be put down to the treatment rather than to who happened to be in which group.
One group may receive a placebo: something that looks like the treatment but has no active ingredient. Placebos are only used when it is safe to do so, and you will be told before you join whether the study uses one. In many studies neither you nor the team knows which group you are in until the end. That is called blinding.
Who keeps watch
Before a trial can begin, an independent ethics committee, known in the U.S. as an institutional review board, must approve it. Large trials also have a data monitoring committee that looks at results as they come in and can stop a study early if there is a safety concern. Studies of new medicines in the U.S. are overseen by the Food and Drug Administration.