A drug that looks, tastes, and smells completely indistinguishable from a real drug, but does not contain any active pharmaceutical ingredient, is called a "placebo" or "fake drug”. Conversely, a " real drug" is one that contains the active ingredients.

When a drug is used, the body responds to the drug according to its effects. However, the human body sometimes reacts in the same way as when the actual drug is used, even if the drug is a placebo, simply because the drug was used. This is called the "placebo effect”.

In a clinical trial, we may have one person (person A) take the actual drug and another person (person B) take a placebo, and evaluate each person's physical response, because if the drug works for person A but not for person B, we can evaluate that the drug seems to be effective.

Thus, placebos play a very important role in determining whether the data obtained in a clinical trial is due to the drug's ingredients or to the placebo effect. In addition, to ensure that these data can be evaluated without preconceived judgments, the distinction between the actual drug and the placebo is not made clear to the subjects taking the medication or to the clinical trial staff.