What is the placebo effect and the blinding

How are clinical studies conducted?

Because the results of studies have a huge impact on how patients are treated, they must be trusted.

The results of clinical studies have a major impact on how patients are treated now and in the future. If it turns out in the course of a study that a new treatment approach is more suitable than the previous one, the previous one is quickly replaced and no longer used. For this reason, one must be able to rely on the results of clinical studies.

The prerequisite for reliable results is that studies are carefully planned and, if possible, protected from external influencing factors, as these could lead to a falsification of the results.

Influencing factors that can lead to a falsification of the study result are, for example: age, general state of health, severity of the disease or other diseases. There are now various measures that minimize the influence of such factors on the study result. They ensure that the starting conditions for the different groups of participants are approximately the same. The influencing factors thus have an equal effect on the groups of participants.


Randomization means the random allocation of study participants to the treatment groups.

The study participants are usually divided into two different groups before the start of the study. One group receives the new treatment method and the other either the previous standard treatment or a dummy drug (placebo).

Randomization means that the allocation to the treatment groups is random. This is usually carried out by a central control center, which is responsible for organizing the study. The random allocation ensures that the influencing factors affect the groups equally. This prevents, for example, only younger and less ill patients from ending up in one group and only older and more seriously ill patients ending up in the other group. In this case, the results from the two groups would hardly be comparable.


Placebos are dummy drugs that contain no active ingredient.

If no currently used standard therapy is available, drugs are often compared with dummy drugs (placebos). Outwardly, these are usually indistinguishable from the correct drugs, but do not contain any active ingredient. The advantage of a comparison with a placebo is that the effect that can be attributed to the active ingredient can be easily differentiated from psychologically induced effects.

The placebo effect is the phenomenon that placebos can also have positive effects on the course of the disease, even though they do not contain any active substance. Psychological effects are mainly held responsible for this phenomenon.


By blinding is meant that the patient does not find out which treatment group he belongs to while participating in the study.

The patient's expectation of a therapy has a major influence on the effect that can be achieved through it. Just the belief in receiving a well-effective medicine can lead to an improvement in the condition of the disease in these patients. In order to keep the influence of these attitudes and expectations of the patients on the study results as low as possible, the study is blinded. This means that it is kept secret which treatment group the patient belongs to during the study. If a placebo is used in the study, the patient does not know whether he is receiving the right drug or a placebo during the study. The group membership is only disclosed when the study is completed.

Double-blind study

In double-blind studies, neither the doctor nor the patient knows which treatment group the patient belongs to.

The attitudes of the doctor can also have an influence on the results of the study. For example, by subconsciously treating patients who are given the right drug differently than patients who are given a placebo. To avoid this, there are so-called double-blind studies in which neither the patient nor the doctor knows which group a patient has been assigned to.

However, under certain circumstances (for example when severe side effects occur), the information on group membership will be disclosed by the study center.

Safety during the study

If the safety of the participants cannot be adequately ensured during a study, the study will be discontinued.

The process and the work of the study center will be continuously reviewed throughout the study. Under certain circumstances, a clinical trial may be discontinued while it is in progress. This occurs, for example, if in the course of the study it is found that the treatment method of one group is far superior to the other. In this case, it would not be justifiable to continue treating one group with the proven poorer therapy. The study will then be stopped so that all patients can be treated with the better therapy. Another example of early study termination would be if serious side effects are observed during the study. In this case, the study is terminated in order to rule out any risk to the patient.

Here you can find out more about the requirements that clinical trials must meet to make them as safe as possible for patients.

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Written by the Viomedo editorial team