Clinical Trial Phases
Clinical trials of new treatments are most commonly conducted by the companies that will ultimately market the drugs. There are four phases:
Phase 1
Phase 1 trials involve very small numbers of people and are used to test the drug’s safety and to help determine a dose that people will tolerate. Such trials may give indications that the treatment is likely to be beneficial, but they are too small to provide solid evidence.
Phase 2
Phase 2 trials involve more people and aim to provide the first conclusive evidence that a drug will be a useful treatment for human disease. The dose may also be fine-tuned at this stage.
Phase 3
Phase 3 trials are large trials usually involving hundreds or even thousands of people. These trials are designed to gather all of the evidence a company needs to have a drug approved by the government, including information about both positive outcomes and negative side effects.
Phase 3 trials frequently compare a new treatment to a placebo (a fake treatment) to ensure that any benefits or problems seen are due to the treatment alone. A new treatment may also be compared to any established treatments that exist for the disease.
Phase 3 trials are usually blinded, which means that the neither the person receiving the treatment nor the person giving it know which treatment is being used (new treatment, fake treatment or other established treatment). This prevents any biases from affecting the results.
Phase 4
Phase 4 trials are done after the drug has received approval to gather additional information about the drug’s optimal use.