Clinical Trials


Understanding clinical trials

Clinical trials explore whether a treatment is safe and effective

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Why clinical trials are important

They help us see what will work in medicine

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Types of clinical trials

Each type of trial has a different purpose

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Understanding clinical trials

A clinical trial is a particular type of research that explores whether a medical strategy, treatment or device is safe and effective for humans.


Involving patients, healthy volunteers or both, a clinical trial is one part of a long and careful research process. Clinical trials provide researchers with the opportunity to potentially find better treatments for others in the future, as well as offering hope for many people.

What do clinical trials do?

Clinical trials are used to help find out if a treatment:

Is safe to use

Has any side effects

Works better than a standard treatment

Helps make you feel better

Why clinical trials are important

Although all new drugs, treatments and devices are rigorously tested in the laboratory they must also go through clinical trials so more can be found out about their potential benefits or risks.


We need clinical trials to find out what does and doesn’t work in medicine and healthcare. A new treatment is not always better than existing treatments. Clinical trials are therefore very important as they can provide essential answers.

Why do people take part in clinical trials?

From a survey of 5,701 patients, the top perceived benefits were seen as:1

Advancing science and treatment
Helping to improve or save lives
Helping to improve my condition

1. Accessed June 2017.

Types of clinical trial

Clinical trials come in many different formats, these are called phases.


Each phase has a distinct purpose and helps researchers answer a variety of questions on safety, effectiveness and the right dose to use.

Phase one trials are used to test the safety of a new medicine and to identify any side effects. They are also used to calculate the right dose of the treatment to use. This part of the trial is known as “dose-ranging”. Dose-ranging can also be carried out in later phases of clinical trials.
A Phase one trial is the first time a new medicine is tested in humans and is usually carried out with a small group of healthy volunteers or sometimes patients.
Phase two trials test the new treatment on a larger group of people (100–300). This time however, the participants are usually patients who have the particular condition the new treatment is for. This helps the researchers find out whether and how well the treatment works and further evaluates its safety.
Phase three trials are only carried out if the treatment has passed Phase one and two. This type of trial often lasts more than a year and involves testing the treatment in an even larger group of patient volunteers (1,000–3,000). They are used to gather more information about the safety and effectiveness of the treatment and to compare it against an existing treatment or a placebo. A placebo is a harmless dummy treatment, which has been designed to look, smell and taste like the treatment being tested. A placebo is often called a ‘sugar pill’.
Phase four trials are carried out once a new treatment has passed all of the previous phases and has been approved by the regulatory authorities, such as the FDA (Food and Drug Administration) in the US and the EMA (European Medicines Agency) in Europe. Researchers use Phase four trials to track a treatment’s safety and to find out more about a treatment’s risks or benefits and its optimal use. This type of trial can also help identify any rare side effects from the treatment.
Unfortunately not all clinical trials will be positive. Some of the studies will discover that the treatment being tested does not work, has worse side effects than existing treatments, or that it is no better than an existing treatments. It is important to remember that this kind of information is still useful for researchers and doctors and that it will help patients in the future.