Informed consent means that before you can join a trial, the researchers must fully explain the study to you and obtain your agreement to take part. The researchers must explain a number of important things about the trial, such as its purpose, the treatment that will be tested, the number of clinic visits, possible benefits and harms, and so on.

A Patient Information Sheet will normally be provided explaining all these things.
Informed consent takes place after all of the important facts about the trial have been explained, when you say that you understand these facts and you agree to enter the trial.

In the case of children, a parent or guardian has to give consent for them to take part in a trial, although older children should also understand and agree themselves.

You will usually be asked to sign a consent form, to show that you understand what has been explained to you. It is meant to show that you have made your decision not only of your own free will, but also in full possession of the facts. You are fully entitled to change your mind after you have signed this form.