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The phases of a clinical trial

Researchers spend many years developing new treatments or medicines in the laboratory before involving people. They then plan the clinical trial to progress in a series of steps called phases. Every phase considers whether the risks outweigh the benefits. Information gathered in each phase determines whether the study can move on to the next phase, and whether the drug or treatment is approved for use.

There can be up to four phases, but not all clinical trials go through every phase. See below for a description of different phases.

Watch this video to find out more about the different phases.

How clinical trial phases work

Phase 1 – Safety

Phase 2 – Effectiveness

Phase 3 – Comparison

Phase 4 – Follow-up

Video: The 4 phases of clinical trials

In this video, Dr Elizabeth Hovey explains the four different phases of a clinical trial.

Podcast: Making Treatment Decisions

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Key resource

Download a PDF booklet on this topic.

Understanding Clinical Trials and Research

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This information was last reviewed in January 2022. View who reviewed this content.

A/Prof Brett Hughes, Senior Staff Specialist, Medical Oncology, Royal Brisbane and Women’s Hospital and The Prince Charles Hospital, and Associate Professor, The University of Queensland, QLD; Christie Allan, Clinical Trials Lead, Cancer Council Victoria, VIC; Dawn Bedwell, 13 11 20 Consultant, Cancer Council Queensland, QLD; Joanne Benhamu, Senior Research Nurse, Team Lead, Lung, Colorectal and Palliative Care Trials, Parkville Cancer Clinical Trials Unit, Peter MacCallum Cancer Centre, VIC; Louise Dillon, Consumer; Sabina Jelinek, Clinical Nurse Research, St John of God Murdoch Hospital, WA; Chloe Jennett, Program Coodinator, Cancer Research, Cancer Council NSW; Carmel McCarthy, Consumer; Alison Richards, Research Unit Manager, Medical Oncology Clinical Trials Unit, Flinders Medical Centre, SA; Prof Jane Ussher, Translational Health Research Institute (THRI), School of Medicine, Western Sydney University, NSW; Prof Janette Vardy, Medical Oncologist, Concord Cancer Centre, and Professor of Cancer Medicine, The University of Sydney, NSW.

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How many people take part (participants)
What it aims to do (purpose)	first study in people tests safety of new treatment finds the safest dose and the best way it can be given, identifies side effects and checks how the treatment works with other medicines or food (interactions) often includes people with different types of cancer
How it works	participants are given a fixed dose and watched closely for side effects the dose is often small in the first group of participants, and then gradually increased in the next groups until any side effects outweigh the potential benefits
More information	may involve overnight stay in hospital for monitoring people may benefit but often don’t see big improvements

How many people take part (participants)
What it aims to do (purpose)	builds on the results of the phase 1 trial continues to test safety of the new treatment begins to assess how well the new treatment works on the disease
How it works	often focuses on one type of cancer the participants may be put into separate groups and given different treatments (randomised controlled trial) or they may all have the same experimental treatment (non-randomised trial)
More information	people often have treatment as an outpatient

How many people take part (participants)
What it aims to do (purpose)	tests if the new treatment is better than the best currently available treatment (standard treatment) compares side effects, survival and quality of life collects information that allows new treatments and existing treatments to be used in new ways or for different diseases
How it works	uses two or more treatment groups – experimental and control usually groups are randomised and sometimes blinded a placebo may be used for comparison runs over a longer period of time
More information	some phase 3 trials help the Therapeutic Goods Administration (TGA) work out whether to approve a new drug for use in Australia

How many people take part (participants)
What it aims to do (purpose)	identifies how well the new treatment works when used more widely in the real world monitors the long-term benefits and risks looks for other uses of the treatment sometimes known as an expanded access study
How it works	carried out after the treatment has been approved by the TGA usually run by pharmaceutical companies that make the product some people are able to get early access to new drugs before the cost is covered by the Pharmaceutical Benefit Scheme (PBS)
More information	not all treatments go through a phase 4 clinical trial phase 4 trials are less common than phase 1–3 trials