Phases of Clinical Trials


Health Economics

  • Clinical trials on humans are conducted in stages, prior to which tests on animals for toxicity will have been completed. Each phase has a different purpose. In Phase I trials, researchers test a new drug or treatment in a small group of healthy people (usually less than 100) for the first time to evaluate its safety, determine a safe dosage range, and identify side-effects. In Phase II trials, the treatment is given to a larger group of people (100+) with the disease to see if it is effective (proof of principle) and to evaluate its safety further. In Phase III trials, the treatment is given to large groups of people (1000-3000) preferably in double-blind trials (sometimes multi-centre) to confirm effectiveness, monitor side-effects, compare it to commonly used treatments and collect information that will allow the drug or treatment to be used safely. There are also Phase IV trials: post-marketing studies yielding additional information about the drug's risks, benefits and optimal use.