What is a Clinical Trial?

A clinical trial (also called clinical study) is a research study that explores whether different treatments are safe and how well they work. Some trials involve healthy members of the public. Others involve patients who may be offered the option of taking part in a trial during their care and treatment. People who take part in clinical trials are volunteers. They may also be called “participants” or “subjects.”

Clinical trials are carried out to try to answer specific questions about health and illness. A treatment can be a drug, medical device, medical procedure, or a change in a person’s behaviour such as diet or exercise.

In a trial, a treatment can be compared to a placebo (a substance with no pharmacological activity) or to existing treatments to determine whether it is effective.

Phase 1 (sometimes referred to as Phase I)

Normally the first trials in humans are performed as phase 1 trials with a small number of healthy volunteers (20-80). It is normal to have several phase 1 trials, each evaluating different questions such as how safe it is, the appropriate dosage and identifying side effects.

Phase 2 (sometimes referred to as Phase II)

Phase 2 trials test the treatment in a larger group of people (typically 100-300) to better measure the safety and side effects and to see if the treatment has a positive effect in patients.

Phase 3 (sometimes referred to as Phase III)

Phase 3 trials usually have a larger number of patients (approx. 1000 to 3000). They aim to find out how well the treatment works and how long the effects last. These trials compare the effects of the treatment with the standard treatment (if there is one) or placebo. Phase 3 trials also determine how common and serious any side effects or risks are.

Phase 4 (sometimes referred to as Phase IV)

Phase 4 trials are conducted once a treatment has been approved for use and is on the market. The aim of a phase 4 trial is to provide additional information about the risks and benefits of the treatment.

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