Who can be part of a clinical trial?

Due to the wide variety of trials taking place, almost anyone can take part in a clinical trial. Trials can involve people of all ages, from children to the elderly, and with all types and stages of a disease or condition. Taking part in a trial is completely voluntary and participants can withdraw at any time with no adverse effects on the quality of their medical treatment or relationship with their doctor.

Some trials need healthy participants to test the safety of new interventions or tests (particularly in early stage trials). In these trials, healthy participants can be compared with patient participants. They receive the same test, procedure or drug that the patient group receives and researchers can compare the effects and side effects of the new test, procedure or drug between the two groups.

Many trials need participants who have the disease or condition that the new intervention targets. Patient participants test the new intervention to see what effect it has on their disease or condition.

Why you might not be able to take part

All clinical trials have guidelines about who can take part. These guidelines are called inclusion and exclusion criteria. Criteria that must be met in order to allow someone to take part in a clinical trial are ‘inclusion criteria’; criteria that prevent someone taking part are ‘exclusion criteria’. The criteria may be based on age, gender, the type and stage of a disease or condition, previous treatment history and other medical conditions. Inclusion and exclusion criteria aim to ensure that the trial will produce useful and reliable results and contribute to the safe conduct of the study.

Sometimes, it is not possible for a volunteer to be involved in a particular trial. For example:

  • some trials seek people with certain diseases and conditions, while others need healthy people
  • the disease or condition may need to be at a particular stage
  • participants may not be allowed to receive another treatment at the same time
  • some trials need people of a certain age
  • there may already be enough people in a particular category who have joined the trial.

Medical tests

Before participants join a trial, they may need to have tests (such as a blood test) to see if they can take part. These tests may also allow the researchers to know more about a person's health before they start trial treatment, so that, at the end of the trial, they can tell if there has been an improvement. During the trial, participants are likely to have more tests to see whether the treatment is working.