About clinical trials

Clinical trials usually move through a series of stages called phases, each phase is designed to answer different questions about the treatment being tested.

• Phase 1 focuses on safety. It involves a small group of volunteers and looks at how the body handles the treatment and what dosage is safe.
• Phase 2 studies whether the treatment works for the condition it’s meant to help, while continuing to monitor safety.
• Phase 3 compares the new treatment to the best currently available options in a larger group of patients. Results from this phase are used to help regulators decide whether the treatment should be approved for public use.
• After approval, Phase 4 studies may continue to track the treatment’s long-term safety and real-world benefits.

These phases are used by regulatory authorities to make sure any new medicine has been tested carefully before it becomes widely available. For further information see FDA and EMA.

Before joining any clinical trial, a participant must go through a process called informed consent, which is designed to help them fully understand what taking part will involve. All major health regulators require that this process is clear, thorough, and focused on protecting the participant. Informed consent is not just about signing a form; it is an ongoing conversation between the participant and the research team. The participant must receive understandable information about the purpose of the study, what will happen during the trial, possible risks and benefits, alternative options, their rights, and who to contact with questions. Informed consent must be voluntary, based on sufficient, accessible information, and tailored to individual needs.

Informed Consent Forms (ICFs) and Participant Information Sheets (PIS) are written in age-appropriate language and approved by ethics committees for use in the clinical trial. For further information, see NHS HRA and CT Toolkit.

The informed consent process places the participant, at the centre of the clinical trial empowering them to make decisions that are right for them. For further information, see EMA.

When children or young people take part in clinical trials, the consent process must be handled with extra care. A parent or legally authorized representative must give permission before a child can join a study.

Regulatory authorities highlights the need for clear, age appropriate explanations and notes that assent from minors should be sought whenever possible, ensuring they are involved to the extent that matches their maturity and understanding. Further information can be found here.

Once all trial phases are complete, regulators review the evidence to decide whether the treatment is safe, effective, and of high enough quality to be approved for use in patients. Each regulatory authority conducts a thorough scientific assessment before allowing any new medicine to be prescribed. These agencies follow similar principles to ensure decisions are based on strong, trustworthy clinical data. For further information, see EMA.