Randomised, controlled trials & placebo
In most cases, a clinical trial is randomized. This means patients are allocated to a specific group, usually automated, to make sure the different groups are as similar as possible. Each group than receives a different kind of treatment (active compound or placebo/standard treatment). This is called the control group. Researchers randomize trails to ensure they have no bias that could affect the results.
When a randomized trial has a control group, it is called a randomized controlled group. Some trials have more groups to test variations, for example in the height of the doses. When there is no standard treatment available for the control group to have, a placebo-group can be included: a medicine or procedure is given that has no therapeutic effect.
A placebo may only be used when no standard treatment is available. From an ethical perspective you cannot withdraw care according to the latest Standards of Care and it is unethical to give a placebo to a group of patients who are in need for treatment, so ethics committees will not grant permission to trials designed this way.