Phases of a clinical trial

Not all treatments go through a phase 0 trial.

Phase 0 clinical trials:
·       aim to speed up the development of promising drugs by testing them in people rather than animals, which gives more reliable results.
·       use small, therapeutic doses of a drug or treatment to see what it does in people.
·       use doses too small to treat your tumour, but you’re less likely to have side effects.

These are usually the earliest trial of a treatment in people, after testing in the laboratory
Phase 1 clinical trials tend to be carried out in specialised clinical research units rather than hospitals. They recruit only a few people and last several months.

Phase 1 clinical trials aim to find out::
·       whether the treatment is safe
·       what’s the right dose to use
·       whether it has any side-effects.

Treatment is:
·       initially given at a low dose to a small group of people, who may be healthy volunteers
·       then, if the first group experienced no serious side-effects, given to another group at a higher dose.
·       This process is repeated with other groups, until the ‘maximum tolerated dose’ or MTD is determined.

Patients will receive optimum care and attention while in the unit.

Not all treatments tested in phase 1 will make it to phase 2.

Phase 2 clinical trials use larger groups of patients (up to about 100) and can last for a couple of years.

They aim to find out:
·       more about the safety and side-effects of the treatment
·       whether the new treatment does what’s hoped (referred to as its efficacy), for example, shrink the tumour, keep it away for longer, make the patient feel better.

They:
·       often compare the new treatment to an existing treatment or to a dummy drug, known as a placebo
·       may be a randomised trial – where people are put into the different treatment groups at random.

Most drugs unfortunately don’t make it to phase 3 because they turn out to be ineffective, unsafe or have intolerable side-effects in phase 2.

Phase 3 clinical trials often take place in many hospitals across different countries. They are carried out on larger groups (several thousand patients), who are usually ill, and often last for several years.

Phase 3 trials aim to find out:
·       if the new treatment works better than the existing, ‘standard’ treatment
·       whether it produces fewer side-effects.

They:
·       Compare 2 groups of patients with similar characteristics to see if the new treatment is better
·       Are often ‘randomised, blind trials’, meaning that patients are not aware whether they are taking the new treatment or a placebo. This ensures that the trial results are not biased and can be trusted.

Read more about randomised trials.


If successful, the treatment can be put forward to the appropriate authorities for approval to be licensed for use. This approval process can take several years.

Phase 4 trials are conducted after a drug has been shown to be effective and has been licensed to treat an illness.

Phase 4 trials:
·       aim to find out what happens when the drug is given to thousands of people in the general community
·       assess any long-term risks and benefits and any rare side-effects of the drug.