We have been writing about Clinical Trials in my last two posts, Clinical trials (Part 1) and Clinical Trials (P-2), we have described the terms which are very important in carrying out a clinical trial. This post again, we explain few more terms; Placebo effect and Blinding. So here they are;

4. Placebo Effect

The patients may respond positively when they are looked after by concerned, helpful and keen medical staffs. This positive response is a completely psychological outcome.  This is called the placebo effect, which can be defined as the pure psychological, beneficial effect, that a medical treatment can have on a patient. This effect is not physiological and is short-lived. It cannot be attributed to the intervention but to the emotional impact that the process has on the patient. A medical treatment need to show its effectiveness apart from its psychological impact or the placebo effect.

The placebo effect can be measured by administering a placebo to participants who do not receive the test treatment (the control group) when no standard treatment exists. Placebo is an inactive medication with the same taste, texture, etc. as the active medication but has no intended theraupetic value. It could be sterile water, saline solution, sham surgery, inert injections or even a sugar pill.

Placebo effect: A placebo makes the patient psychologically feel better

Placebo effect is hence the phenomena in which some people experience benefits after the administration of an inactive substance or sham treatment. In other words, if the participants show change in the readings (of the factor been analyzed) on receiving the placebo similar to the ones in test group, it could be all because of the placebo effect, and the drug is really not having great physiological effect.


Placebo-controlled trials have a placebo group as control and are quite common. As mentioned they are used only when no standard treatment exists. The patients are blinded (or masked) for the fact that they have received placebo and not the active medication but are told of this possibility before deciding to take part in the study. The use of placebo has its own scope for debate on ethical grounds.

Read More in detail about placebo effect here.

5. Blinding/ Masking

We have seen how bias can arise in the clinical trials and affect the outcome of these important studies (Clinical Trials (P-2), topic Randomization). To summarize again the possible bias can be introduced by the participants, researchers, assessors (who analyze the measurements) and so on. Most of these problems, can be solved to a certain extent by not revealing the treatment which a particular participant will receive. This concealing the identity of the treatment administered to the participant is called Blinding or Masking.

1. Open-trial 2. Single-blind 3.Double-blind 4.Triple-blind

Blinding / Masking can be defined as a procedure in which one or more parties in a clinical trial are kept unaware of which treatment a patient/participant receives i.e. which treatment arms participants have been assigned.

Types of blinding:

Single blind: In this, only one party is blinded, usually the participant. This prevents the psychological negative effect which may arise in the patients receiving placebo. Hence this helps in avoiding the performance bias of the patient. The patient may even quit the study if he is revealed about being treated with the placebo, due to lack of interest.

Example of single blind clinical trial.

Double blind: Here both the participant and the study staff are blinded. The staff may be biased either about the subject or the outcome and may show favorism during alloting thepatients to treatment arms. Sometimes despite randomization, there are chances the staff knowing or predicting the random sequence. Also, if the researcher and/or the hospital staff is aware of the treatment, they may not show the same interest in the patients being treated with placebo, or the ones in notreatment group. In such cases the staff maybe kept blinded along with the patient. This can be achieved by keeping a code for the treatment.

Triple blind: In this type of study, participants, study staff and the the data analysts, all are blinded. The data analysts or the assessors can be subconsiously influenced and score the control group participants differently. This is specially more of a bother in case of subjective outcomes, like degree of pain, degree of redness, etc, which cannot be measured using instruments.

Example of a triple blind study.

Open label or Open trial: In this type of trials, no blinding is used or even possible and all the partiesare aware of the treatment groups. Hence both the researchers and participants know which treatment is being administered. This study may be appropriate for comparing two very similar treatments to determine which is most effective. It may be unavoidable under some circumstances, such as comparing the effectiveness of physical therapy sessions. The open trials may be randomized (ie theselection of patients/volunteers in two group is random). It can also be uncontrolled, with all participants receiving the same treatment.

Examples of difficult to blind clinical trials: Trials of interventions such as massage or physiotherapy. Here’s an example.

This is all for this post. Hope u like this post, if yes please comment, like and share!!

Also follow us on Facebook, Twitter, Instagram or send an email to thebiotechnotes@gmail.com.

Have a nice day!

Thank you!!

Read other posts by The Biotech Notes:

The Lactose Operon

Sickle Cell Disease.

Coombs test.


Katzung, B. G., Masters, S. B., & Trevor, A. J. (2012). Basic & clinical pharmacology. New York: McGraw-Hill Medical.