Clinical trials are typically divided into several phases, which are designed to answer specific scientific questions about a new treatment. The number and duration of phases can vary depending on the type of treatment being studied and the specific goals of the trial.
Here is an overview of the different phases of clinical trials:
Phase 1: In this phase, a small group of healthy volunteers or patients (typically 20-80 people) are given the experimental treatment to determine its safety and side effects, and to establish a safe dosage range. Phase 1 trials are usually the first time that a new treatment is given to humans.
Phase 2: In this phase, the experimental treatment is given to a larger group of patients (typically 100-300 people) to further evaluate its safety and effectiveness. Phase 2 trials may also examine different doses of the treatment or compare it to a standard treatment.
Phase 3: In this phase, the experimental treatment is given to an even larger group of patients (typically 1,000-3,000 people) to confirm its effectiveness, monitor side effects, and compare it to standard treatments. Phase 3 trials are usually the last stage of testing before a treatment is considered for approval by regulatory agencies.
Phase 4: After a treatment has been approved and is being used in clinical practice, Phase 4 trials (also called "post-marketing surveillance") may be conducted to monitor its long-term safety and effectiveness in a larger population.
It's worth noting that not all clinical trials follow all four phases. Some trials may skip certain phases if the treatment is deemed to be particularly promising or if there is a pressing medical need for it. Additionally, there are other types of clinical trials, such as Phase 0 and Phase 1b, that may be conducted in certain situations.