How clinical trials work

Health research often involves new medical interventions such as new drugs or devices, new surgical techniques or other treatment procedures. Researchers test some of these in a clinical trial with human beings. Learn who conducts clinical trials and what’s involved in running one.

Who conducts clinical trials


Researchers who conduct clinical trials may work from:

  • hospitals and other medical research institutions
  • universities
  • pharmaceutical, medical device and biotechnology companies
  • specialised medical clinics
  • a combination of these.

Clinical teams

A clinical trial team usually includes doctors and nurses and may also involve:

  • clinical and non-clinical managers
  • trial investigators (medical and non-medical practitioners)
  • trial coordinators (nurses, research assistants)
  • pharmacists
  • other healthcare professionals such as pathology and radiology
  • clinical trial sponsors (commercial, investigator initiated, trial networks and universities)
  • social workers
  • biostatisticians
  • trial coordinators and monitors.

At the start of the trial, the clinical team takes initial measurements and a medical history from participants. The team gives participants clear information about what the trial is about, what to expect in the trial and what they need to do.

During the trial members of the trial team carefully monitor each participant.

Ethical guidelines and consent

National ethics guidelines, laws and codes of conduct govern clinical trials in Australia. This protects trial participants and ensures research integrity. These standards include the:

Learn more about the TGA’s clinical trials guidance.

An ethics committee must approve all clinical trial research. In Australia, a human research ethics committee (HREC) usually provides this approval. HRECs check that any research involving human participants meets ethical standards and guidelines, such as the national statement.

Ethics committee review includes review of the documents that will guide the way researchers conduct the clinical trial. One of these documents includes the information that researchers must provide to you before you choose to participate in the trial.

If you are participating in a clinical trial, researchers must tell you:

  • the research objectives
  • what they expect of you
  • about any risks or potential inconveniences you might experience during and after the trial.

They will then give you a Participant Information and Consent Form (PICF) that explains this to review and sign.

As a clinical trial progresses, researchers may report the results of the trial at scientific meetings, to medical journals and to various government agencies. When they do this, they do not disclose the names or personal details of trial participants.

Find out what you need to know as a trial participant.

Trial protocols

Clinical trials follow a plan or set of rules, known as a protocol, that describes how the research should be done. A good protocol ensures that trials are as safe as possible and measure the right things in the right way so that the results are meaningful.

For example, a protocol describes:

  • who is eligible to take part in the trial
  • the methods, tests and procedures researchers will use
  • the interventions researchers will use and how they will deliver them
  • the length of the study, what information researchers will collect and any follow up with participants in the research.

Control groups

To determine if an intervention is successful, and not just due to a natural recovery, researchers need to compare the intervention they are studying to another intervention, to standard care or to a placebo. Participants in a clinical trial will be put into 1 of 2 or more groups:

  • group 1 is given the new intervention being studied
  • group 2 is given an intervention that is already in use, other standard care or a placebo.

In this scenario, group 2 is known as the ‘control group’.

Some clinical trials include more than 2 groups. Each group receives a different combination of interventions, but a trial will almost always include a control group.

The clinical trial compares what happens in each group. The results have to be different enough between each group to prove that the difference has not just occurred by chance.

Researchers can end the clinical trial early if one of the groups shows significant improvement over the control group, without any serious side-effects. This gives them the chance to change the design of the clinical trial so that more patients get the opportunity to receive the new intervention.

Types of comparison

Comparing a new intervention with a standard intervention

Researchers often compare a new intervention with a standard or commonly used intervention that they already know to be helpful. This makes it possible to determine whether the new intervention works better than an existing one.

Comparing a new intervention with a placebo

In some clinical trials, researchers compare a new intervention with a placebo. A placebo is an inactive treatment, such as a sugar pill. It looks the same, or is used the same way, as the interventional substance but has no known effect on the participant.

If the patients who received the intervention have a better outcome compared to patients who received the placebo, this suggests that the intervention was effective.

Researchers do not use placebos if not getting an effective treatment would put the patient at risk. This applies, for example, in research into treatments for serious diseases. Researchers must tell people if they will be using placebos in the trial before the person agrees to participate.

Placebo effect

Research has shown that if you think and believe you are going to get better, you are more likely to do so. If you take something you believe to be an effective medicine, your symptoms may improve. Reassurance from a doctor or other healthcare professional also helps some people to feel better. This is known as the ‘placebo effect’.

When researchers use a placebo in a clinical trial, it looks the same as the new medication they are studying, so you don’t know which one you are taking. Researchers take the placebo effect into account when designing clinical trials. They ensure that the number of people involved in the trial is large enough to compensate for any possible placebo effects.

Number of people in a clinical trial

The effect of an intervention may vary between people. Researchers must test promising interventions on a large enough number of people to see if the effect is meaningful and not due to chance.

For example, if 7 out of 10 people improve with a new intervention, this could be due to chance. However, if 700 out of 1000 people improve, then researchers can be reasonably confident that the new intervention is effective. Researchers use mathematical calculations to work out how many people they need for a particular trial and whether the results are statistically significant.

Later phases of trials require larger numbers of participants.


Many trials compare the effects of an intervention using 2 or more groups of participants. The groups need to be as similar as possible except for the intervention received (or not received). This means that any differences in outcomes are due to the differences between interventions and not the differences between groups.

To ensure that there is no bias during the selection of the different groups for a clinical trial, computers randomly allocate participants to each group. This means that those running the trial haven’t influenced the allocation.

Blinding trials

‘Blinded’ or ‘masked’ trials are those that do not identify who is receiving the new intervention and who is not.

In a ‘single-blind’ clinical trial, participants do not know which intervention they are receiving, but the researchers and medical staff do.

In a ‘double-blind’ clinical trial, neither the researchers organising the trial nor the participants know who is receiving which intervention.

Blinding helps to reduce the effects of bias when comparing the outcomes of the interventions.

If either researchers or participants know who is receiving the new intervention, this knowledge can influence what they report. Participants who think that they are receiving a new intervention may be very hopeful about its effects, or not want to let down the researcher. For this reason, they may exaggerate benefits and minimise side effects.

Likewise, researchers may allow their hopes for a new intervention to unconsciously influence how they record the effects.

In an emergency where your doctor needs to know which intervention you are receiving to provide the care you need, the blinding can be 'broken' and they can find this out.

When a trial is completed

When a clinical trial is complete, researchers examine all the information collected during the study to decide whether to:

  • continue to the next phase of the clinical trial
  • seek approval for general use by the relevant authorities.

Once researchers have shown that a new intervention is safe and effective, it may become part of standard treatment for the disease or condition.

It can take some time for researchers to examine and analyse trial results. For large trials involving thousands of people, that may take place over several years. There may be a delay before the full results are known.

If you have taken part in a trial and have asked to know the results, researchers should make them available to you directly. Researchers usually publish results of all completed studies in reports, or papers in scientific journals.

Find more information on procedures relating to the end of a clinical trial in the National Standard Operating Procedures for Clinical Trials.

Date last updated:
  • About clinical trials