A placebo is a sugar pill that does not cause harm or good. In many trials testing an investigational medication, a proportion of the people recruited will receive a placebo without knowing if they are receiving the investigational medication or the placebo.
When you may not get a placebo
The decision about whether to use a placebo in a clinical trial is based on how serious the illness is, whether an existing treatment is available, and other considerations that ensure a high standard of ethics.
For example:
In trials where a treatment is already available for the disease or condition, or in the case of serious illness, the available treatment (or standard of care) is usually used instead of a placebo.
Where there are no current treatments, trials may have one group getting the new treatment with another group getting a placebo.
The group of patients given the placebo or standard of care is called the control group, as they are the patients receiving the current standard and what the new drug will be compared against.