The phases of a clinical trial

Glossary

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 up to four steps called phases. 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. See below for a description of the different phases.

To find out how to get involved in a clinical trial or another type of study, see Joining a study.

Learn more about:

What are Phase 0 trials?

These are exploratory studies, sometimes referred to as “microdosing” or “pilot studies”. These trials are less common, and are used to test how the body responds to an experimental drug and whether it is worth moving on to a Phase 1 trial. A small dose of the drug is given once or for a short time to 10–15 people, sometimes to healthy volunteers. These trials do not offer any direct benefit to participants.

How the different phases work

Phase 1

Participants
10–100
Purpose
  • first study in people
  • tests safety of new treatment
  • finds the safest dose and the best way a treatment can be given
  • identifies side effects
  • studies how the intervention works with other medicines or food (interactions)
How it works
  • participants are given a fixed dose and watched closely for side effects
  • if no side effects, dose is increased in next group of participants, this continues until noticeable side effects appear
 More info
  • patients sometimes benefit from having the new treatment but great improvements in their condition are uncommon

Phase 2

Participants
100–300
Purpose
  • builds on the results of Phase 1
  • continues to test safety of a drug
  • begins to assess how well a new treatment works on the disease
How it works
  • often focuses on one cancer type
  • all participants receive the same experimental treatment
  • sometimes randomised controlled trial – i.e. participants are put into separate groups and given different treatments, which are then compared to see how well they treat the disease
 More info
  • people often have treatment as an outpatient, but occasionally need to stay overnight in hospital for monitoring

Phase 3

Participants
100s–1000s
Purpose
  • tests if the new treatment is better than the standard treatment
  • compares side effects, survival and quality of life
  • assesses whether the risks outweigh the benefits
  • 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
  • placebo may be used for comparison
  • runs over a long period of time
 More info
  • Phase 3 trials help the Therapeutic Goods Administration (TGA) assess whether a new drug should be registered for use in Australia

Phase 4

Participants
1000s
Purpose
  • identifies how well treatment works when used more widely
  • monitors the long-term benefits and risks
  • looks for other uses of the drug or treatment
How it works
  • carried out after a treatment has been registered by the TGA
  • usually run by pharmaceutical companies that make the product
  • may be used as a way to provide early access to a drug after TGA approval but before Pharmaceutical Benefit Scheme (PBS) approval
  • sometimes called expanded access study
 More info
  • not all treatments go through Phase 4 studies
  • they are less common than Phase 1–3 trials

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This information was last reviewed in July 2018
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