Does the Understanding of Placebo Mechanisms Compensate for the Loss of Efficacy Associated With Open Label Placebo (PLACETHIC)

Does the Understanding of Placebo Mechanisms Compensate for the Loss of Efficacy Associated With Open Label Placebo

Does the Subject's Understanding of Underlying Placebo Mechanisms Compensate for the Loss of Efficacy Associated With the Disclosure of the Use of a Placebo

The investigators are investigating whether, when given detailed information about underlying placebo mechanisms and pain, subjects will have a response similar to that of those subjected to a procedure in which they receive a conventional placebo treatment (associated with deception). STUDY DESIGN: This is a non-inferior parallel, controlled and randomized, single blind trial. POPULATION: The investigators will include in the study 126 subjects without known pathology. Participants will then be divided into 2 groups on a randomized basis. METHODOLOGY: Each subject will undergo three sessions of Cold Pressure Test (CPT), a cold pain stimulation method: calibration, condition of interest (conventional placebo or educated placebo) and control. The investigators' main judgment criterion is be the difference in pain intensity experienced on the visual analog scale between the CPT control and the CPT under the condition of interest. This study will allow the investigators to rule on the non-inferiority of an educated open label placebo compared to a conventional placebo in the context of an acute painful stimulation.

2 groups : Educated open label placebo And Conventional placebo Each of the subjects will undergo the Cold Pressure text procedure under the condition of interest and a control.

Only the subjects in the the conventional placebo group will be masked. In the educated open label placebo group, subjects will be aware that the cream is inert.

These subjects will undergo all the same procedures as in the control group. But before the placebo CTP, they will watch a short movie explaining placebo mechanisms. While applying the placebo cream, they will be told that the cream is inert (placebo), efficient to decrease pain caused by cold and the mechanisms seen in the movie will take place.

These subjects will watch a video on hand washing. While applying the placebo cream, they will be told that this cream is effective to decreased pain caused by cold.

Educational movie on placebo mechanisms : animated video, duration : 12 minutes. It will be followed by the CPTs : experimentally induced pain by keeping the non dominant hand in cold water (1° Celsius) for a limited time. The duration of immersion is personal and calibrated to be around to ensure that the intensity of pain will be homogeneous (around 7/10 on the visual analogue scale with no treatment)

Animated video, duration : 11 minutes. It will be followed by the CPTs : experimentally induced pain by keeping the non dominant hand in cold water (1° Celsius) for a limited time. The duration of immersion is personal and calibrated to be around to ensure that the intensity of pain will be homogeneous (around 7/10 on the visual analogue scale with no treatment).

Evaluated with a Visual Analogue Scale (VAS) from 0 to 100 mm, with a non inferiority margin at 10 mm and a standard deviation at 22 mm.

At the end of the CPT procedure, within 30 seconds after the removal of the hand from the CPT cold water tank.

Evaluated thanks to the respiratory frequency collect with a PneumoTrace belt through LabChart software.

Evaluated thanks to the automatic blood pressure monitor (both systolic/diastolic blood pressure, heart rate)

The perception of the investigator will be evaluated by a visual analogue scale "perception of the investigator".

At the end of the study, when all CPT procedures have been carried out, within 10 minutes after the last immersion

Perception of the research hypothesis with the Rubin Questionnaire. Perceived Awareness of the Research Hypothesis " (PARH) wich is a scale of 4-item quantitative self-report method for measuring the potential influence of demand characteristics in research situations

At the end of the study, when all CPT procedures have been carried out, within 10 minutes after the last immersion

Safety measure to insure blood pressure does not exceed 150/90mmHg (both systolic/diastolic blood pressure, heart rate)

Inclusion Criteria: Person affiliated to Social Security Informed consent, written and signed by the subject. Exclusion Criteria: Persons referred to in Articles L1121-5 to L1121-8 of the Public Health Code (CSP), which corresponds to all protected persons: pregnant women, parturient women, nursing mothers, persons deprived of their liberty by judicial or administrative decision, persons subject to a legal protection measure, cannot be included in clinical trials. Persons with a pathology against indicating the use of CPT experimentally induced pain : Any pathologies affecting the venous, arterial or lymphatic system Diabetes Cardiac disorders Asthma Frostbite Epilepsy Arthritis Lupus erythematosus Allergy to Cremafluid® cream Person with concomitant treatment that modifies sensitivity to pain, chronic or acute at the time of the experiment, such as analgesics, psychotropic drugs or anti-inflammatories.

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