5. Phases Of Clinical Trials Click to return to the Clinical Trial main page There are four phases of clinical trials to ensure that new treatments or procedures are safe and effective for the public. Phase 0 Testing a low dose of treatment to check it isn't harmful. Phase 0 trial tests are the earliest trials of a treatment in humans, with a small group participating (10 - 20 people). The phase studies do not examine the drug's effectiveness but its safety. It tests a minimal dose of medicine on a tiny group of often healthy people, looking to see if it behaves the way it did in the laboratory studies, what side effects it has, and what happens to the medicine in the human body. Phase I Finding the best dose, what side effects happen and how the treatment is processed in the body. A Phase 1 trial tests an experimental treatment on a small group of often healthy people, looking at safety, side effects, the correct medicine dosage and what happens to the medicine in the human body (20- 80 Participants). A Phase 2 trial involves a larger group of people. It focuses on determining the effectiveness of a treatment for a specific disease or condition and evaluating safety and short-term side effects. This phase can span several years and typically includes 100 to 300 participants. Researchers may need to adjust the dosage or criteria for participant selection. They may repeat Phase 2 trials to ensure they have the right group of participants and the most suitable drug before progressing to larger-scale testing. Phase II Checking the best dose, finding out more about side effects and seeing how well it works. Phase III Comparing the new treatment to the standard treatment or a dummy medicine (placebo). In a Phase 3 trial, researchers gather more information about a medication's safety and effectiveness by studying different populations and dosages. They also observe how the medication performs in real-life situations, for example, when combined with other medicines, like antibiotics, to treat a chest infection. Phase 3 trials involve hundreds to 3000 participants and can last three to five years. The research team evaluates the medication or intervention's long-term effectiveness and safety during this phase. If the Medicines and Healthcare Regulation Authority (MHRA) agrees that the trial results are positive and results prove benefit, it will approve (license) the experimental medicine or device for the use of the general population. Phase IV Finding out more about the long-term benefits and/or side effects A Phase 4 trial for medicines or devices takes place after the MHRA approves their use (licensed). The trial monitors a device or medicine's effectiveness and safety in larger or diverse populations for more extended periods of time. Researchers are looking at the long-term risks and benefits of the new drug or intervention, how it affects people in real life, and the rarer side effects. Phase 4 is much longer than the previous one and can take 10-20 years. Navigate to other pages about clinical studies: 1. Clinical Trials Explained: Learn the basics 2. Clinical Trials Process: Start to Finish 3. Types of Clinical Trials 4. Accuracy and Safety in Clinical Trials 5. Phases Of Clinical Trials 6. Clinical Trial: Key Participant Information 7. Clinical Trials Community Questions Manage Cookie Preferences