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What is a Double Blind Placebo Control Study?

Updated: Aug 22, 2019

Some medical professionals we at CannaMedU have had discussions with indicate the lack of scientific studies on Medical Cannabis as the reason they are not on board with recommending it as medical treatment. This statement can be confusing to those of us who are not highly trained medical professionals or scientists. There are clearly thousands of scientific articles and observational studies on PUB-MED featuring cannabinoids, terpenes, CBD, and THC. The difference is that Medical professionals understand the value of a Double-Blind Placebo Control Study (DBPCS) which

“remain(s) the most convincing research design in which randomly assigning the intervention can eliminate the influence of unknown or immeasurable confounding variables that may otherwise lead to biased and incorrect estimate of treatment effect. Also, randomization eliminates confounding by baseline variables and blinding eliminates confounding by co-interventions, thus eliminating the possibility that the observed effects of intervention are due to differential use of other treatments. The best comparison is placebo control that allows participants, investigators and study staff to be blinded. The advantage of trial over an observational study is the ability to demonstrate causality.” (Misra, 2012)

The design of an effective DBPCS involves two groups of study participants, neither of which knows if they are receiving the real treatment or the placebo treatment. The placebo is designed to closely resemble the actual treatment. The research professionals who are conducting the study also do not know what individual patients will receive the placebo or the actual treatment, this is what double blind means. The assignment of treatment each patient receives is handled by randomization, which prevents bias in patient care.

Another caveat of a DBPCS is that the treatment and the placebo must not test more than ONE variable at a time and the study MUST BE DUPLICATABLE with similar results. “Properly executed, such designs ensure a study's internal validity and allow differential group outcomes to be attributed to the active treatment. These controlled trials generally yield more conservative outcomes than open trials and case reports and establish efficacy in pharmaceutical research.” (Rains, 2005)

In summary, in order for a study to be considered DBPC there are several factors that must be present.

1. There must be a control group and an experimental group.

2. The patients must be randomly and blindly assigned their treatment.

3. The placebo treatment must be as close as possible to the experimental treatment

4. The study must test only ONE treatment option.

5. The study must be duplicatable and produce similar results to be valid.

My next blog posting will discuss the challenges in implementing the DBPCS with Medical Cannabis.

Misra, Shobha. “Randomized Double Blind Placebo Control Studies, the ‘Gold Standard’ in Intervention Based Studies.” PubMed, National Center for Biotechnology Information, U.S. National Library of Medicine, July 2012,

Rains, JC, and DB Penzien. “Behavioral Research and the Double-Blind Placebo-Controlled Methodology: Challenges in Applying the Biomedical Standard to Behavioral Headache Research.” PubMed, US National Library of Medicine, National Institutes of Health, May 2005,

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