[Medical] Phases of Clinical Trials

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What trial phases are

Clinical trials are divided into different stages, called phases. The earliest phase trials may look at whether a drug is safe or the side effects it causes. A later phase trial aims to test whether a new treatment is better than existing treatments.

There are 3 main phases of clinical trials – phases 1 to 3. But some trials have an earlier stage called phase 0, and there are some phase 4 trials done after a drug has been licensed.


Phase 0 trials

Phase 1 trials are usually the earliest trials of drugs in people. But your doctor might ask if you would like to join a phase 0 study. These studies aim to find out if a drug behaves in the way researchers expect it to from their laboratory studies.

Phase 0 studies usually only involve a small number of people and they only have a very small dose of a drug. The dose of the drug is too small to treat your cancer, but the types of things researchers are looking for include


Whether the drug reaches the cancer

How the drug behaves in the body

How cancer cells in the body respond to the drug


You might have extra scans and give extra samples of blood and cancer tissue (biopsies) to help the researchers work out what is happening.

Because the dose of the drug used in phase 0 trials is so small you won’t benefit from the drug. But you are also less likely to have side effects.

The main aim of these studies is to speed up the development of promising new drugs. Testing them in very small doses in humans rather than in animals can be more reliable and means scientists get useful information more quickly.



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