Phase 1 Trials

Clinical trials involving new drugs are commonly classified into four phases. Each phase of the drug approval process is treated as a separate clinical trial. The drug-development process will normally proceed through all four phases over many years. If the drug successfully passes through Phases 1, 2, and 3, it will usually be approved by the national regulatory authority for use in the general population.

  • Phase 1: Screening for safety
  • Phase 2: Establishing the testing protocol
  • Phase 3: Final testing
  • Phase IV: ‘Post-approval’ studies

In Phase 1 trials, researchers test an experimental drug or treatment in a small group of people (20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.


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